U.S. President Donald Trump on Labor Day hit back at Richard Trumka, president of the United States’ largest federation of labor unions, after Trumka said on Sunday that the president’s policies had hurt American workers.

Trumka, who is head of the American Federation of Labor and Congress of Industrial Organizations (AFL-CIO), said on Fox News Sunday of Trump’s policies: “Unfortunately, to date, the things that he’s done to hurt workers outpace what he’s done to help workers.”

The AFL-CIO president cited changes to the tax code that encourage companies to outsource jobs, the administration’s failure to produce an infrastructure program, and its overturning of regulations, including some protecting health and safety.

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On Monday, which is the national Labor Day holiday, Trump tweeted that Trumka had represented his union “poorly.”

“Some of the things he said were so againt the working men and women of our country, and the success of the U.S. itself, that it is easy to see why unions are doing so poorly,” Trump added.

In follow-up tweets, the president hailed economic growth, adding: “The Worker in America is doing better than ever before!”

On Sunday, Trumka had also questioned Trump’s Saturday tweet that there was no need to keep Canada in the North American Free Trade Agreement (NAFTA). The president warned Congress not to meddle with the trade negotiations or he would terminate the trilateral trade pact altogether.

“It’s pretty hard to see how that would work without having Canada in the deal,” Trumka said on Sunday, noting that the economies of Mexico, the United States and Canada were heavily integrated.

Trumka is a highly influential figure on trade issues and his support will likely be necessary for the passage of any legislation on trade promoted by the administration.