The chief executive of Walmart, the world’s largest retailer, criticized President Trump in front of his 1.5 million American employees, widening a rift between the White House and the business community that has been growing since the weekend’s violence in Charlottesville, Va.

“As we watched the events and the response from President Trump over the weekend, we too felt that he missed a critical opportunity to help bring our country together by unequivocally rejecting the appalling actions of white supremacists,” Douglas McMillon, the Walmart C.E.O., wrote in a letter to employees late Monday.

The rebuke from Mr. McMillon came as six other business leaders stepped down from presidential advisory councils — including two late on Monday, the C.E.O.s of Intel and Under Armour — citing their own values as the primary motivation for distancing themselves from Mr. Trump.

The president hit back at his critics in the business world during a news conference at Trump Tower Tuesday. He spent several minutes lashing out at some of the most prominent executives in the country, saying that those who left his councils were “not taking their jobs seriously” and were “leaving out of embarrassment.”