HOUSTON, Jan 28 (Reuters) - Negotiators for Exxon Mobil Corp and the United Steelworkers union (USW) are discussing a contract proposal that could receive a ratification vote by workers locked out of a Beaumont, Texas, refinery since May 1, 2021, a union official said on Friday.

The members of USW Local 13-243 in Beaumont could vote on the contract proposal, if one is agreed to by negotiators, sometime in February, said Bryan Gross, USW International representative.

Gross declined to offer details about the proposal under negotiation.

Exxon spokesperson Julie King said the company has been negotiating with the union for a year.

"Exxon Mobil has actively engaged in good faith negotiations with the United Steelworkers union at the Beaumont refinery and lubricants plant since January 2021," King said on Friday. "The company’s offer remains available for ratification."

Exxon's offer was rejected in a vote by the members of Local 13-243 in October.

Exxon began the lockout because the union had issued a strike notice to the company during negotiations for a new agreement.

The company said a strike could cause a disruption to operations at the 369,024 barrel-per-day refinery and adjoining lubrication oil plant.

The two sides were unable to reach an agreement prior to the lockout because the company insisted on removal of job seniority provisions, which union officials have said provide workers a say in job assignments.

Exxon said its offer would give it flexibility to operate in even low-margin environments.

Exxon has previously said the lockout would end when a contract was ratified or the union was removed from the refinery.

A vote on the union's removal was conducted by the U.S. National Labor Relations Board (NLRB) in November and December, but the ballots were impounded on Dec. 29, by the board so it could review charges filed by the USW alleging Exxon undertook the lockout to force the union's removal.

(Reporting by Erwin Seba; Editing by Leslie Adler and Aurora Ellis)