A Union Blitzed Starbucks. At Amazon, It’s a Slog.

Roughly six weeks after successful union votes at two Buffalo-area Starbucks stores in December, workers had filed paperwork to hold union elections in at least 20 other Starbucks locations nationwide.

By contrast, since the Amazon Labor Union’s victory last month in a vote at a huge warehouse on Staten Island, workers at just one other Amazon facility have filed for a union election — with an obscure union with a checkered past — before promptly withdrawing their petition.

The difference may come as a surprise to those who believed that organizing at Amazon might follow the explosive pattern witnessed at Starbucks, where workers at more than 250 stores have filed for elections and the union has prevailed at a vast majority of the locations that have voted.

Christian Smalls, the president of the independent Amazon Labor Union, told NPR shortly after the victory that his group had heard from workers in 50 other Amazon facilities, adding, “Just like the Starbucks movement, we want to spread like wildfire across the nation.”

The two campaigns share some features — most notably, both are largely overseen by workers rather than professional organizers. And the Amazon Labor Union has made more headway at Amazon than most experts expected, and more than any established union.

But unionizing workers at Amazon was always likely to be a longer, messier slog given the scale of its facilities and the nature of the workplace. “Amazon is so much harder a nut to crack,” John Logan, a labor studies professor at San Francisco State University, said by email. The union recently lost a vote at a smaller warehouse on Staten Island.

To win, a union must get the backing of more than 50 percent of the workers who cast a vote. That means 15 or 20 pro-union workers can ensure victory in a typical Starbucks store — a level of support that can be summoned in hours or days. At Amazon warehouses, a union frequently would have to win hundreds or thousands of votes.

Organizers for the Amazon Labor Union spent hundreds of hours talking with co-workers inside the warehouse during breaks, after work and on days off. They held cookouts at a bus stop outside the warehouse and communicated with hundreds of colleagues through WhatsApp groups.

Brian Denning, who leads an Amazon organizing campaign sponsored by the Democratic Socialists of America chapter in Portland, Ore., said his group had received six or seven inquiries a week from Amazon workers and contractors after the Staten Island victory, versus one or two a week beforehand.

But Mr. Denning, a former Amazon warehouse employee who tells workers that they are the ones who must lead a union campaign, said that many didn’t realize how much effort unionizing required, and that some became discouraged once he conferred with them.

“We get people saying how do we get an A.L.U. situation here? How do we do that like they did?” Mr. Denning said, adding: “I don’t want to scare them away. But I can’t lie to workers. This is what it is. It’s not for everyone.”

At Starbucks, employees work together in a relatively small space, sometimes without a manager present to supervise them directly for hours at a time. This allows them to openly discuss concerns about pay and working conditions and the merits of a union.

At Amazon, the warehouses are cavernous, and workers are often more isolated and more closely supervised, especially during an organizing campaign.

“What they would do is strategically separate me from everyone in my department,” said Derrick Palmer, an Amazon employee on Staten Island who is one of the union’s vice presidents. “If they see me interacting with that person, they would move them to a different station.”

Asked about the allegation, Amazon said it assigned employees to work stations and tasks based on operational needs.

Both companies have accused the unions of their own unfair tactics, including intimidating workers and inciting hostile confrontations.

Organizing drivers is an even greater challenge, partly because they are officially employed by contractors that Amazon hires, though labor organizers say they would like to pressure the company to address drivers’ concerns.

Christy Cameron, a former driver at an Amazon facility near St. Louis, said the job’s setup largely kept drivers from interacting. At the beginning of each shift, a manager for the contractor briefs drivers, who then disperse to their trucks, help load them and get on the road.

“It leaves very little time to talk with co-workers outside of a hello,” Ms. Cameron said in a text message, adding that Amazon’s training discouraged discussing working conditions with fellow drivers. “It was generally how they are highly against unionizing and don’t talk about pay and benefits with each other.”

Amazon, with about a million U.S. workers, and Starbucks, with just under 250,000, offer similar pay. Amazon has said that its minimum hourly wage is $15 and that the average starting wage in warehouses is above $18. Starbucks has said that as of August its minimum hourly wage will be $15 and that the average will be nearly $17.

Despite the similarity in pay, organizers say the dynamics of the companies’ work forces can be quite different.

At the Staten Island warehouse where Amazon workers voted against unionizing, many employees work four-hour shifts and commute 30 to 60 minutes each way, suggesting they have limited alternatives.

“People who go to that length for a four-hour job — it’s a particular group of people who are really struggling to make it,” said Gene Bruskin, a longtime labor organizer who advised the Amazon Labor Union in the two Staten Island elections, in an interview last month.

As a result of all this, organizing at Amazon may involve incremental gains rather than high-profile election victories. In the Minneapolis area, a group of primarily Somali-speaking Amazon workers has staged protests and received concessions from the company, such as a review process for firings related to productivity targets. Chicago-area workers involved in the group Amazonians United received pay increases not long after a walkout in December.

Ted Miin, an Amazon worker who is one of the group’s members, said the concessions had followed eight or nine months of organizing, versus the minimum of two years he estimates it would have taken to win a union election and negotiate a first contract.

For workers who seek a contract, the processes for negotiating one at Starbucks and Amazon may differ. In most cases, bargaining for improvements in compensation and working conditions requires additional pressure on the employer.

At Starbucks, that pressure is in some sense the union’s momentum from election victories. “The spread of the campaign gives the union the ability to win in bargaining,” Mr. Logan said. (Starbucks has nonetheless said it will withhold new pay and benefit increases from workers who have unionized, saying such provisions must be bargained.)

At Amazon, by contrast, the pressure needed to win a contract will probably come through other means. Some are conventional, like continuing to organize warehouse employees, who could decide to strike if Amazon refuses to recognize them or bargain. The company is challenging the union victory on Staten Island.

But the union is also enlisting political allies with an eye toward pressuring Amazon. Mr. Smalls, the union president, testified this month at a Senate hearing that was exploring whether the federal government should deny contracts to companies that violate labor laws.

On Thursday, Senator Bob Casey, a Pennsylvania Democrat, is introducing legislation seeking to prevent employers from deducting anti-union activity, like hiring consultants to dissuade workers from unionizing, as a business expense.

While many of these efforts may be more symbolic than substantive, some appear to have gotten traction. After the Port Authority of New York and New Jersey announced last summer that it was awarding Amazon a 20-year lease at Newark Liberty International Airport to develop an air cargo hub, a coalition of community, labor and environmental groups mobilized against the project.

The status of the lease, which was to become final by late last year, remains unclear. An Amazon spokeswoman said that the company looked forward to “continued engagement in the state” and that it was confident the deal would close.

A spokeswoman for Gov. Phil Murphy of New Jersey indicated that the company might have to negotiate with labor groups before the deal could go forward. “The governor encourages anyone doing business in our state to work collaboratively with labor partners in good faith,” the spokeswoman said.

Karen Weise contributed reporting.