(Bloomberg)—Amazon.com Inc. holds a commanding lead in a historic election to determine whether workers at its warehouse in Bessemer, Alabama, will become the first in the U.S. to join a retail union.

Vote counting resumes Friday, with about half of the 3,215 ballots still untallied. The math is daunting for the Retail, Wholesale and Department Store Union: Amazon had 1,100 no votes to 463 yeses for the labor group when U.S. officials halted work Thursday evening.

With Amazon ahead in the tally, the union telegraphed its intentions to appeal the result.

“Our system is broken, Amazon took full advantage of that, and we will be calling on the labor board to hold Amazon accountable for its illegal and egregious behavior during the campaign,” said Stuart Appelbaum, RWDSU president. “But make no mistake about it; this still represents an important moment for working people and their voices will be heard.”

Citing documents obtained via a Freedom of Information Act request, the RWDSU accused the company of “corrupting the election” by pressuring the U.S. Postal Service to install a mailbox on Amazon property in an effort to make employees to cast their ballots there rather than someplace more free of company surveillance. Employees have also said that Amazon used mandatory group meetings and one-on-one discussions to predict harmful consequences if they unionized.

Amazon has said that it hosted “information sessions” so employees could “understand the facts” about unionization, and told the Washington Post that the mailbox was a “simple, secure, and completely optional” way to make voting easier. The company declined to comment on Appelbaum’s accusations.

The National Labor Relations Board is tallying the ballots from its office in nearby Birmingham and beaming the process live to the media via Zoom. Approximately 5,800 workers were eligible to vote, and turnout was roughly 55%.

The election officially ended on March 29, but Amazon and the union spent several days reviewing sealed individual ballots for such irregularities as problematic signatures, ripped envelopes and ineligibility to vote. Contested ballots—which numbered about 500 and were disputed at a 4-1 ratio by Amazon, according to the union—were to be reviewed later only if there were enough to swing the outcome. (Reuters earlier reported the 500 total.)

The fiercely fought mail-in election lasted seven weeks and attracted national attention. The last unionization vote among Amazon employees failed in 2014, when a group of fewer than 30 machinists in Delaware declined to join the International Association of Machinists and Aerospace Workers.

A RWDSU victory in Bessemer could eventually force Amazon into contract talks with the union, which is focused on improving working conditions for warehouse employees. The company notes that its $15 an hour starting wage is more than double the federal minimum and that it pays health benefits.

Amazon’s sales and profit soared during the pandemic when millions of shoppers stampeded online. The outbreak put a spotlight on the safety and working conditions of essential workers at supermarkets, big-box stores and online fulfillment centers. Amazon is No. 1 in the Digital Commerce 360 Top 1000.

In Bessemer, employees overwhelmed by the working pace and afraid of catching Covid-19 contacted the union, setting in motion a vote that’s already seen as a watershed for Amazon and organized labor. If the RWDSU prevails, the unionizing drive could spread to other Amazon facilities, some of which are already seeing stirrings of labor activism. A loss for the union would be a setback for the U.S. labor movement, which has been in decline for decades.