By Erwin Seba

BEAUMONT, Texas (Reuters) -Hundreds of union workers at Exxon Mobil Corp (NYSE:).’s Beaumont, Texas, oil refinery began voting on Tuesday on a sweetened contract offer that potentially could end a standoff over job assignments.

Exxon locked out the plant’s 650 union workers on May 1, replacing union-represented workers with managers and temporary staff as it pushed for a contract that gives it control over how jobs are assigned ahead of a major expansion, and sets a freeze to some workers’ pay.

Union members have not been paid for almost six months.

There were about 200 United Steelworkers union members gathered in the first of three groups to vote on the six-year contract proposal, a Reuters witness said. Union officials have urged members to reject the “sub-par” offer that they said could lead to job losses.

“Exxon Mobil is not trying to negotiate a contract, they are trying to dictate a contract,” said union worker Richard Landry, 59, who spoke on Monday night during a break from picket duty.

“I think a lot of people are mad at the company and some people are upset at the union,” said Landry, who declined to discuss how he will vote. “We’ll see how it goes.”

The dispute has grown increasingly bitter. Exxon this week accused the union of “aggressively” opposing its offer and falsely claiming there could be job cuts and saying the lockout would end Nov. 1. Union officials accuse Exxon of being behind a decertification campaign to remove the union.

All 650 workers represented by the United Steelworkers union local 13-243 are eligible to vote during meetings throughout the day. Results are expected late Tuesday.

The contract proposal would give Exxon control over staffing of a new crude distillation unit that would add 250,000 barrels per day (bpd) capacity in 2024, making Beaumont the largest U.S. oil processing plant by volume. The refinery’s current capacity is 369,024 bpd.

If workers approve the contract, they still would vote next month on a worker-submitted petition to oust the union from the plant. The U.S. National Labor Relations Board has set a mid-November vote date. It would first consider a union charge that Exxon improperly aided the petition before releasing results.

An Exxon spokesperson was not immediately available to comment on the vote timing. The NLRB did not reply to a request for comment.

“Refining continues to contend with a challenging business environment,” Exxon said in an online post urging ratification of the contract. “We are trying to position Beaumont for a long, successful future.”