The United Auto Workers union announced plans to have as many as 46,000 hourly workers strike General Motors (GM) - Get Report at midnight ET Sunday after talks toward a new contract failed to produce an agreement.

"We stood up for General Motors when they needed us most. Now we are standing together in unity and solidarity for our members, their families and the communities where we work and live," UAW Vice President Terry Dittes said in announcing plans for the first major U.S. auto-industry walkout in more than a decade.

The two sides remain far part on issues ranging from benefits to how long it takes workers to reach the top of GM's union pay scale.

General Motors said in a statement that it's offered the workers a package worth more than $7 billion. "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," the company said. "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."

The automaker put forth a detailed explanation of its proposed offerings in the negotiations on Sunday around noon that include what GM called "best-in-class wages and benefits" such as wage increases, an "improved" profit sharing formula, ratification payment of $8,000, and new health coverage for autism therapy care, chiropractic care and allergy testing.

It also promised investments in eight facilities in four states, the opportunity to become the first union-represented battery cell manufacturing site in the U.S. and additional new vehicle and propulsion programs.

If the strike goes forward, however, unionized General Motors workers will join 850 UAW-covered maintenance employees who struck at midnight Saturday at several GM plants in Michigan and Ohio, but who technically work for Aramark (ARMK) - Get Report

GM spokesman David Barnas told TheStreet earlier that "we have contingency plans in place to cover any potential disruptions" caused by the strike by Aramark workers, who provide housekeeping and janitorial services at five facilities.

But a strike by thousands of autoworkers could cost GM more than $1 million per hour at each plant that is idled, according to the Ann Arbor-based Center for Automotive Research. Workers would also take a financial hit with strike pay of just $250 a week for those who show up to picket.

The UAW strike fund totaled more than $721 million at the end of 2018, but a widespread walkout across GM's 35 plants could drain that quickly.

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(This is a developing story. Check back for updates.)

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