Over the weekend, the number of oil workers on strike increased by nearly 1,400 after employees at two BP oil refineries in Ohio and Indiana walked out, joining the nearly 4,000 already on strike, ThinkProgress reported.

The strike, which began on February 1, is being led by the United Steelworkers Union which called for the walk-outs after negotiations with Shell Oil broke down. As oil prices steadily decreased, rather than take a loss in the billions of dollars in profit they make, oil companies instead chose to lay off workers.

So far, replacement workers have crossed the picket lines at all of the refineries affected by the strike but one.

The first nationwide strike since 1980 has now spread to 11 plants total and, in addition to those in Ohio and Indiana, includes workers in California, Kentucky, Texas, and Washington.

A post on the local Toledo, Ohio union’s Facebook page read that the “strike is NOT about money,” that it is “about addressing safety issues that have been ignored for way too long … 138 workers were killed on the job while extracting, producing, or supporting oil and gas in 2012,” a number that was “more than double” the 2009 total.

“Management cannot continue to resist allowing workers a strong voice on issues that could very well make the difference between life and death for too many of them,” said USW International President Lew W. Gerard in a statement.

Shell spokesman Ray Fisher said that the company wasn’t aware of any unfair labor practice charges filed against it, reported Reuters.

“We regret that we have been unable to reach a mutually satisfactory agreement with the USW prior to contract expiration,” said Fisher. “We remain committed to resolving the remaining issue through collective bargaining at the bargaining table.”

USW Vice President Gary Beevers, head of the union’s National Oil Bargaining Program (NOBP) said that Shell “has also failed to accept ‘no-retrogression’ language in the contracts requiring the acceptance of previous industry agreements,” said TP.

“We will not relinquish 50 years of progress in NOPB bargaining,” Beevers said, citing “flagrant contracting” as having a negative impact on workers’ health and safety.

Representing about 30,000 workers at 200 sites in America, USW is currently negotiating a national contract for 63 plants. A full USW strike could disrupt nearly 64 percent of US fuel output, according to Bloomberg, although the current strike is not expected to affect current fuel prices.