Exxon Mobil Corp on Tuesday welcomed an upcoming vote by workers at its Beaumont, Texas, refinery on a new contract offer, saying its terms ensure the refinery can stay profitable over the long-term.

Nearly 600 workers represented by the United Steelworkers union were locked out of the 369,024 barrel-per-day (bpd) refinery and adjoining lubrication plant last May 1 and have been without paychecks.

"We are pleased that our represented employees will have another chance to vote," said Exxon spokesperson Julie King. "Our offer provides long-term stability, including job protections and wage progressions for employees."

A USW official said the union is withholding recommendations on the proposal but wants members to decide on the twice-sweetened offer. A membership vote is scheduled for Feb. 21.

USW Local 13-243 said in a statement it would "continue to hold Exxon Mobil management accountable and pursue our charges with the National Labor Relations Board (NLRB) over the company's serious unfair labor practices."

The proposal would give Exxon new control over job assignments, something it has sought as part of an expansion at the refinery. The expansion would make Beaumont its largest by oil-processing capacity in the United States.

Exxon has said the changes in job seniority were necessary so it could be competitive even in low-margin environments.

The workers rejected a similar contract proposal in October.

The new offer makes Martin Luther King Day a paid holiday, clarifies language about a union committee, and provides a job description for operators in the lubrication oil plant, Exxon has said.

Still to be determined is whether the USW will continue to represent the plant's workers. The U.S. National Labor Relations Board (NLRB) held a vote on decertifying the union late last year. Results of that vote have been withheld while the NLRB reviews USW unfair labor practice charges alleging Exxon began the lockout to force the union's removal.