Congrats! You formed a union. Now comes the hard part.

Union membership in the US has been in decline for decades, but there’s recently been a potential shift. Seventeen corporate Starbucks locations in the US have voted to form a union since the end of last year, and another 170 or so are slated to vote in the coming weeks and months — all in an industry where unionizing is rare. And in early April, workers at a Staten Island Amazon warehouse also voted for a union, making them the first to organize in a company known for quashing organizing. These successful votes are historic, and they’re an optimistic sign for unions in America.

But while the hard-won union votes might be the most cinematic part, it’s not the end of the story. The lengthy and difficult process of negotiating a contract that benefits workers has only just begun — and its conclusion is far from certain.

To move forward, the union must write a contract with the company, the union and the company must agree on it, and then union members vote on whether they also agree. The process can take anywhere from six months to a few years — and some don’t end with a contract at all. Some 30 percent of unions don’t establish a contract within three years.

The unions representing Starbucks and Amazon workers are off to a good start because, for the most part, their goals are clear. The Amazon Labor Union (ALU) has said its main objectives are to raise wages to $30 an hour, give workers longer breaks, and mostly eliminate mandatory overtime. The first Starbucks Workers United union, at the Elmwood Avenue store in Buffalo, New York, has been in contract negotiations since January 31; it has so far proposed “just cause” firing, better health and safety protocols, and giving customers the option to tip on credit cards. Future proposals include better wages and benefits.

The harder part, experts say, will be getting Amazon and Starbucks to agree on contracts. That’s not for lack of trying on the unions’ part. Rather, unions often face uphill battles with uncooperative companies and toothless labor laws.

Companies can find any number of ways to stall. Amazon is already objecting to the historic Staten Island vote, accusing the union of threatening voters to vote for the union, among other complaints. Starbucks has filed appeals that have delayed union votes but has said it will respect the bargaining process for the stores that have voted to unionize.

Companies are supposed to bargain in good faith, but there’s no timeline on when that should happen, nor are they compelled to agree to the contract. “Our law has no mechanism to force management,” Harry Katz, a professor at Cornell University’s labor relations school, told Recode. If the NLRB, the federal body charged with enforcing labor law, finds that they’re stalling unnecessarily, there’s not much it can do.

It’s clear why many companies stall: It can make unions lose momentum. If years pass without a contract, workers might wonder what the point of the union is at all. Additionally, both Amazon and Starbucks are in industries with high turnover, where the people who were so keen on unionizing might not be in that job long enough to see the contract through, which could potentially stunt the union drive.

The trick for the unions will be leveraging collective action like strikes, as well as public and political pressure, to try to get these employers to agree to a contract.

The Amazon Labor Union, which was created to organize the Staten Island warehouse, is not affiliated with an older union, so it doesn’t have the infrastructure — or cash — from unions that have been collecting dues for years. That means the union, which has so far been funded by crowdsourced money and pro bono help, will have to figure out on its own the labyrinthine processes of writing, negotiating, and enforcing a contract. Most importantly, its lack of affiliation might stymie workers’ ability to strike. Unlike established unions, the ALU doesn’t have a fund to help workers — many of whom make a low hourly wage and might not have cash reserves — get through a protracted strike in which they would forgo their pay.

However, a strike at an 8,000-person warehouse in New York City wouldn’t take that long to be effective, according to Rebecca Givan, a professor at Rutgers’ School of Management and Labor Studies. “It’s possible that fairly modest actions can cause significant disruption,” she said, saying that one-hour or one-day strikes might be enough to push management to agree. It would be very difficult for Amazon to quickly replace striking workers at such a large warehouse.

It’s also possible that the Amazon Labor Union could accept formal or informal help from an existing union, like the Service Employees International Union (SEIU), which is affiliated with the Starbucks parent union. Mary Kay Henry, international president of the SEIU, told Recode in a statement her union would “offer whatever support we can to help workers at Amazon who are fighting for a voice on the job to bargain a better future.” The Teamsters, a union that represents warehouse and distribution workers, may also get involved: On Thursday, ALU leaders Christian Smalls and Derrick Palmer met with Sean M. O’Brien, the Teamsters’ general president. They discussed resources and assistance the Teamsters could provide to help them get their first contract with Amazon, according to a Teamsters spokesperson. Amazon Labor Union did not respond to requests for comment.

Growing union membership across the US, even if it’s not for their own union, is in unions’ best interest, according to Givan. “Amazon is a huge threat to the quality of jobs in the shipping and logistics sector, many of which are Teamsters jobs,” she said.

Part of what has made the Starbucks and Amazon unions successful is their worker-led structure, which has allowed them to largely avoided the criticism that they are outsiders. Starbucks workers themselves are negotiating their contracts — not union lawyers. That will most likely be the case with the Amazon union as well, which is formed entirely of Amazon workers.

The Starbucks union, however, is part of a larger, established union called Workers United. That means it has a lot more resources to guide them through writing and negotiating a contract. That union could also help it with a strike fund if it chose to do so. However, Starbucks stores are a lot smaller than an Amazon warehouse, so a strike at just one of its 9,000 stores would have less of an impact. It would also be relatively easier to replace 20 or so striking baristas.

Something that could work in the unions’ favor is that both Amazon and Starbucks are widely known, customer-facing companies, making it potentially easier for workers to attract political and public boosters.

Politicians from Sen. Bernie Sanders (I-VT) to President Joe Biden have shown support for these union efforts. Public approval of unions is at its highest level since 1965, according to Gallup.

“The whole country is watching and working people everywhere are watching, and they are judging Amazon and Starbucks by their actions,” Givan said.

Public and political union supporters could help pressure the companies to agree to union demands. Perhaps more directly, Starbucks’ own investors have asked the company to remain neutral on unions and quickly come to collective bargaining agreements with stores that unionize.

As to whether the recent spate of successful organizing and current contract negotiations are enough to reverse long-declining union membership, Katz said, “I think it’s going to lead to more [organizing] but I don’t think it’s yet an indication of a massive turnaround.” He added, “We need more Amazons, we need a lot of the Starbucks to get organized. And then we need more signs [of increased unionizing] in the more traditional sectors.”