BAY CITY, Michigan — President Joe Biden reminded Americans he is a “pro-union” president Tuesday as he toured a technology plant to highlight a $300 million expansion, just a day after he sided with business leaders in asking Congress to pass legislation to stave off a crippling rail strike.

The South Korean company SK Siltron is expected to quadruple its production in the coming years at the plant. It’s the latest in a series of massive foreign investments in the U.S. manufacturing and technology sectors trumpeted by Biden amid a push by his administration to on-shore production of key components and products, after the COVID-19 pandemic pushed long-simmering supply chain issues to the brink.

Biden said, as he often does, that he’s been pro-union his entire career, and he’d talked with SK leaders about how American workers were “the best workers in the world, you’re the most qualified workers in the world.”

“The middle class built America, and unions built the middle class,” he said.

His support of unions is a staple of his speeches from warehouses and construction sites around the county. But on Tuesday, it came as he was appealing to lawmakers to override union concerns to prevent a rail strike after an earlier deal Biden helped broker started to fall through. Four of the 12 unions have refused to ratify the agreement, stalling talks and pushing Biden and congressional leaders to get involved to stop what they have said would be a crippling strike during the holiday season. Eight of the unions have ratified the deal.