(Bloomberg) -- Exxon Mobil Corp. said it rejected a labor contract offer from the United Steelworkers union, leaving open the oil giant’s intention to lock out workers at its Beaumont refinery in Texas if the two sides can’t reach an agreement.

The union is still willing to bargain and let its members continue to work while negotiations are going on, a person familiar with the discussions said. In the event of a lockout, however, the union will picket Exxon with signs declaring the lockout is illegal rather than calling a strike.

During a lockout, companies typically bring in temporary workers to operate facilities. Exxon has already advertised for workers to replace union members starting Saturday.

United Steelworkers Local 13-243’s six-year work agreement with Exxon expired Feb. 1 and no new collective bargaining agreement was settled upon for the Beaumont refinery and blending and packaging plant. The union contends Exxon’s offer would enact major changes in the existing contract that impact members’ safety, security and seniority.

Exxon told union representatives Thursday that the union’s latest offer “still includes items that significantly increase costs to the company and that we have consistently expressed cannot be accepted over the last 108 days of bargaining. To be clear, a ratified contract would still avoid any work stoppage.”

The USW and Exxon provided 75-day notices to each other Feb. 15 as required before a lockout or a strike. Exxon has already rejected the union’s offer of a one-year extension and said it will lock out workers if they don’t agree to the company’s current proposal.

Exxon Beaumont union workers have never been locked out. The facility was also not included in a 2015 strike called by the International Union for 12 U.S. refineries and three other plants. The Beaumont refinery can process 359,000 barrels a day of crude.

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