Thousands of United Auto Workers are marching in picket lines outside General Motors plants around the country.
UAW President Ron Gettelfinger said the union launched the strike after what he describes as "one-sided negotiations."
A GM spokesman said the automaker is disappointed in the UAW's decision to call a national strike.
UAW members hit the picket lines late morning on Sept. 24 as drivers leaving GM Assembly Plants honked in support.
"I don't think people are willing to sell out everything we've worked so hard for over the years, so there's going to be some compromise," one union worker assured.
"The company walked right up to the deadline like they really didn't care, and as a result of that we called a strike at 11 a.m.," Gettelfinger explained.
The UAW set the strike deadline Sept. 22, while they continued to negotiate with GM. The union had been expected to ask GM for guarantees of future production at U.S. plants.
Also at issue, how much money GM must put into a trust fund for retiree health care that will be managed by the UAW.
A GM spokesman said the automaker is working with the union to resolve the issues. The UAW hasn't called a nationwide strike during contract talks since 1976, when Ford Motor Company plants were shut down.
There were also strikes at two GM plants during contract negotiations in 1996.
In a statement, a GM spokesman said the company is disappointed that UAW leaders decided to strike.
The two sides are going straight back to the bargaining table.
At a news conference in Detroit, Gettelfinger said job security is the number-one unresolved issue.
He said the union has also been fighting to preserve workers' benefits.