President Donald Trump set his sights on GM for the first time in a while, calling out the U.S. automaker for shrinking its manufacturing presence in America and employing the smallest amount of union workers among the big three automakers in Detroit.

A Bloomberg report released Thursday revealed GM’s 46,000 United Auto Workers trail Fiat-Chrysler by roughly 1,200 and Ford by a whopping 9,000, according to headcounts submitted by each of the companies. It’s the first time GM is behind its competition in union employment since the UAW was founded over eight decades ago.

Trump took to Twitter to rail against the company that was “once the Giant of Detroit,” criticizing the automaker for moving manufacturing to China, and suggesting “they should start moving back to America.”

GM’s 46,000 is actually 2,000 fewer than it had in 2009 after the U.S. government helped bail it out and reorganize after filing for bankruptcy, according to Bloomberg.

Trump’s tweet could increase pressure on the big three automakers as they negotiate a new four-year labor contract with the UAW later this year. The union claims it is going for a bigger slice of compensation after seeing the automakers rake in record profits in recent years.

“They expect to share in the profits for their hard work,” UAW President Gary Jones said in an interview back in July.

GM’s factories in China almost exclusively produce cars and parts for that foreign market, which may not be contributing to the workforce decline. But America’s neighbor to the south could be a much bigger offender.

The auto giant moved production of its Chevrolet Blazer to Mexico, making it the top automaker in that country over Japan’s Nissan Motor Co. The UAW slammed the move, as it forced one factory in Janesville, Wisconsin to shut its doors.