The United States opened the case in May after complaints that workers' rights at a GM pickup-truck plant in Silao in central Mexico were being violated .

The winning "no" vote opens the door for workers to bring in new representation.

The vote at the automaker's Silao plant marks the first major test of labor rules under the United States-Mexico-Canada Agreement.

The new standard gives employees the flexibility to work from anywhere and gives GM access to a broader talent pool.