BEAUMONT, Texas, Oct 19 (Reuters) - Hundreds of union workers at Exxon Mobil Corp"s (XOM.N) Beaumont, Texas, oil refinery were voting on Tuesday on a sweetened contract offer that could end a months-long standoff over job assignments. Exxon locked out the plant"s 650 union workers on May 1, replacing union-represented employees 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 on some workers" pay. read more Union members who cast ballots declined to comment on how they voted. Some noted they had not been paid for almost six months and that unemployment compensation benefits expire this month. There were about 300 United Steelworkers union members who voted by midday on the six-year contract proposal, a Reuters witness said. Union officials have urged members to reject the "subpar" offer they said could lead to job losses. "I think a lot of people are mad at the company and some people are upset at the union," said Richard Landry, who declined to discuss his vote. "We"ll see how it goes." One worker had tears in her eyes while explaining she could not continue to remain out of work, and had voted in favor of the contract, a union official said. The dispute has become 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 on 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 is expected to set a mid-November vote. It would first consider a union charge that Exxon improperly aided the petition before releasing results. read more An Exxon spokesperson was not immediately available to comment on the vote timing. The NLRB did not reply to a request for comment.