By Erwin Seba

HOUSTON, (Reuters) – The United Steelworkers union and Marathon Petroleum lead negotiator (NYSE:) have until Tuesday to reach an agreement on a new contract that will benefit workers at U.S. chemical plants and refineries. Sources familiar with the negotiations said this.

Top USW officials will make the call for a strike to assist some of the thousands who have contracts that expire just after midnight on February 1. However, it could not be announced until Monday night, sources indicated.

If talks are moving towards a new contract, union officials may also consider extending the strike deadline.

After 35 years of work stopspage, the last national strike took place in 2015.

Marathon talks have progressed slow over the past two and half weeks.

Sources said that the company offered only small raises in proposals for pay-raises.

Marathon’s most recent offer was for a 5.5% increase over three years. According to sources, the first offer for pay was made last week and it was for 3% over 3 years.

In 2019, the current contract was negotiated and provided a 11% pay increase for workers in refineries over three years.

A strike will likely follow the same pattern as the 2015 blockade, which started on February 1, 2015. It grew to 12 refineries and accounted for five percent of total oil processing capacity.

Strikes at several of the refineries continued for weeks after the nationwide strike ended in mid-March, with the longest at Marathon’s Galveston Bay Refinery in Texas City, Texas, ending in early July of 2015.

Sources also stated that workers in refineries won’t immediately go on strike if called. Instead, they will continue working until the end of each shift and handover the refinery operations to their replacement workers.