Here’s what to know about the Boeing strike

Boeing is facing a strike that threatens to disrupt plane production, after workers overwhelmingly voted to reject a tentative contract their unions had reached with the company.

Thousands of workers walked off the job in the Seattle and Portland, Oregon, regions Friday, a move that is likely to stall operations at factories where Boeing manufactures most of its commercial planes. While the deal their unions struck with the company Sunday included double-digit pay raises and improvements to benefits, 96% of workers rejected the proposed contract, opting instead to leverage a strike to push for more.

Here’s what else to know about the company’s first strike since 2008:

How many workers are on strike?

Boeing, one of the largest exporters in the United States, employs nearly 150,000 people across the country – almost half of them in Washington state – and more than 170,000 people worldwide. The contract that spurred Friday’s strike covers about a fifth of the company’s employees.

A vast majority of the 33,000 workers under the contract are represented by District 751 of the International Association of Machinists and Aerospace Workers, Boeing’s largest union. Most of that union’s members work on commercial airplanes in the Seattle area. Workers in the Portland area, who are represented by the union’s smaller District W24, are also on strike.

What prompted them to walk off the job?

The leaders of the unions representing the workers on strike reached a tentative deal with Boeing that would have secured raises of 25% over four years, along with improvements to health care and retirement benefits. The company also committed to building its next commercial plane in the Pacific Northwest.

But workers’ overwhelming rejection of that tentative contract reflects their willingness to fight for more, in large part to make up for concessions made in past talks, including the loss of pension benefits a decade ago. The unions started the talks by asking for raises of 40%.

High-profile walkouts across a range of industries – notably, last year’s autoworkers strike – may have emboldened Boeing’s workers to push for more. Workers may also feel they have the upper hand as Boeing tries to move past recent incidents that have raised concerns about the quality and safety of company’s planes.

How will the walkout hurt Boeing’s business?

The strike is hitting the heart of Boeing’s commercial plane manufacturing, most of which takes place in the Seattle area. And it could have ripple effects across the plane maker’s fragile supply chain. The company’s shares fell 3.7% Friday.

The last Boeing strike, in 2008, lasted 50 days. If the current strike lasts about as long, it could cost Boeing at least $3 billion, according to an estimate from Cai von Rumohr, a research analyst at the investment bank TD Cowen. The strike puts at risk Boeing’s plans to increase aircraft production into 2025, Wells Fargo said in a research note.

The ratings firm Moody’s said Friday that it was reviewing Boeing for a debt downgrade in light of the potential effects of the strike. The plane maker’s rating is currently just one rung above the “junk” speculative grade.

Before the strike, Boeing was already dealing with lagging production at its factory in Renton, near Seattle, where it makes its most popular model: the 737 Max. The company has been forced to slow production to make quality improvements after a panel fell off a Max plane during an Alaska Airlines flight in January.

This article originally appeared in The New York Times.