Workers at ExxonMobil’s largest refinery in the US have threatened a possible lockout or strike next month.

United Steelworkers (USW) union had proposed an agreement on health and safety issues with the company in its Baytown refinery in Texas but said that management “refused to accept it in its last, best and final offer given April 15”.

USW said the lack of acceptance prompted them to issue a 60-day notice to terminate the contract and go on strike. The local union agreement contains an “industrial peace” clause that provides a 60-day period where both sides abide by the existing contract while they work to reach an acceptable agreement.

Richard “Hoot” Landry, USW District 13 staff representative said: “We’re confident that an agreement can be reached with ExxonMobil and a strike averted… Our union developed this [health and safety] language to help the oil companies do a better job at process safety so that problems can be detected before they result in fires, explosions, releases and other incidents that impact the health and safety of our workers and the local community.”

Four of ExxonMobil’s refineries have agreed to the health and safety proposal. The union represents around 850 workers at ExxonMobil’s Baytown refinery, chemical plant and laboratory.