Sept. 15 (UPI) — The United Auto Workers union went on strike against General Motors at 11:59 p.m. Sunday after its members failed to reach a new labor agreement.

The union’s 46,000 members at GM plants walked off the job at 31 GM factories and 21 other facilities in the first strike against an automaker in the United States in 12 years.

The union’s contract with GM had expired at 12:01 a.m. Sunday but the strike didn’t occur for another 24 hours.

At 11:59, UAW-GM workers began their strike. https://t.co/UljiErd7yN— UAW (@UAW) September 16, 2019

The UAW announced Sunday morning that its membership will walk out after a formal meeting of the GM Council consisting of local union leaders. The UAW represents nearly 150,000 employees at GM, Ford and Fiat Chrysler. Contract negotiations remain with Ford and Fiat Chrysler.

“We stood up for General Motors when they needed us most,” UAW Vice President Terry Dittes said in a union news release. “Now we are standing together in unity and solidarity for our members, their families and the communities where we work and live.”

The two sides are to meet at 10 a.m. Monday.

On Saturday, Dittes notified General Motors leadership that the union would not agree to extend the Collective Bargaining Agreements after 18 months of negotiations.

“We told UAW GM members that we would stand up for them and their future,” Gary Jones, president of the UAW, said.

GM said the company was prepared to “negotiate around-the-clock” until a tentative labor agreement is reached. But no sessions were scheduled Sunday.

“We presented a strong offer that improves wages, benefits and grows U.S. jobs in substantive ways and it is disappointing that the UAW leadership has chosen to strike at midnight tonight,” General Motors said in a statement. “We have negotiated in good faith and with a sense of urgency. Our goal remains to build a strong future for our employees and our business.”

GM said its offer includes more than $7 billion in investments and more than 5,400 jobs, including in eight facilities in four states.

Also, improvements in wages and benefits include “wage or lump sum increases in all four years, improved profit-sharing formula, ratification payment of $8,000, retain nationally-leading healthcare benefits, new coverage for autism therapy care, chiropractic care and allergy testing.”

The union is seeking “fair wages, affordable healthcare, our share of profits, job security and a defined path to permanent seniority for temps.”

“We have been clear at the table about what GM members have indicated we will accept,” National Bargaining Committee Chairman Ted Krumm of UAW Local 652 said. “We are standing up for what is right. We as local unions will sacrifice to stand up for what we deserve.

“Our members have spoken; we have taken action; and this is a decision we did not make lightly. We are committed to a strong contract at GM that recognizes our UAW members, who make some of the greatest products in the world and make GM so profitable.”

UAW-represented janitors first went on strike early Sunday.

Roughly 850 janitors, who are employed by Aramark but represented by the UAW, went on strike at eight GM plants in Michigan and Ohio.

Union-represented GM workers “reluctantly” crossed picket lines Sunday before the strike authorization, the Detroit Free Press reported.