UAW members and supporters from General Motors' Lordstown Assembly plant, which was idled in March, picket outside GM's headquarters, as 2019 contract negotiations get underway.

DETROIT – United Auto Workers members overwhelmingly granted union leaders authorization to strike during contract negotiations this year with General Motors, Ford Motor and Fiat Chrysler, if needed.

The union on Tuesday announced about 96% of members at each of the automakers supported the action. That's slightly down from negotiations four years ago, when workers at GM and Fiat Chrysler supported a strike by 97% and Ford at 98%.

GM will lead the negotiations, which are expected to be the most contentious in at least a decade amid a slowdown in auto sales, a volatile trade environment and a widening federal probe into union corruption that led to UAW President Gary Jones' home being searched last week by federal officials.

Jones has not been charged as part of the multiyear probe, which has led to the convictions of eight union and company officials affiliated with Fiat Chrysler. Charges were also filed last month against Michael Grimes, a former UAW official assigned to the union's GM department, for allegedly receiving $2 million in kickbacks from UAW vendors.