General Motors workers across the country walked out of plants at midnight Monday as the largest U.S. auto strike in more than a decade got underway.

The United Auto Workers called for the work stoppage after the union failed to reach a new collective bargaining agreement covering some 46,000 workers at dozens of facilities. GM and the union remained far apart in negotiations on Sunday, when UAW leaders converged on Detroit and decided overwhelmingly to strike after their contract expired over the weekend.

Theres no telling how long the impasse could last. Shutting down plants is extremely costly for GM and within weeks could lead to slimming choices for buyers on dealer lots. But workers could start to feel pain, too, as they try to eke by on union strike pay of just $250 per week, a fraction of what the typical employee earns.

The massive strike wasnt hard to see coming . As HuffPost reported in July, GM has been enormously profitable though profits have recently been falling and workers who sacrificed during the auto industrys crisis in 2007 are expecting a bigger share of the gains.

At the same time, GM is intent on keeping its labor costs down as the company braces for a sales slowdown and pumps money into electric and autonomous vehicles.