President Donald Trump kicked off Labor Day on Monday by insulting the leader of the largest labor union federation in the United States.

Trump took aim Monday morning at Richard Trumka, the head of the AFL-CIO, slamming him for having “represented his union poorly on television this weekend.”

“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 wrote, before taking one last dig at Trumka for being, “A Dem!”

Richard Trumka, the head of the AFL-CIO, represented his union poorly on television this weekend. Some of the things he said were so against 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. A Dem! — Donald J. Trump (@realDonaldTrump) September 3, 2018

Trump later deleted the tweet, which contained a spelling error, and replaced it with another that corrected the mistake.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

The post appeared to refer to criticism from Trumka on Sunday of the White House’s strategy in renegotiating the North American Free Trade Agreement.

In an interview with “Fox News Sunday,” Trumka had said the president had “done more to hurt workers than to help” them and said not including Canada in a renegotiated NAFTA would be a bad idea.

“The three countries in North America, the economy is pretty integrated. And it’s pretty hard to see how that would work without having Canada in the deal,” Trumka said.

Trumka’s criticism came after Trump had tweeted that “there is no political necessity to keep Canada in the new NAFTA deal,” adding that, “If we don’t make a fair deal for the U.S. after decades of abuse, Canada will be out.”

Earlier in the week, the U.S. and Mexico struck a trade deal designed to supplant NAFTA.

Many lawmakers, including Republicans in Congress, expressed concern that the agreement would have little utility if Canada can't be included in it.

Trump’s latest remarks about Trumka, whose group has more than 12 million workers, prompted immediate blow back from Democrats, who drew attention to the fact that the posts came on Labor Day.

“Just this morning he was tweeting against Richard Trumka, the head of the AFL-CIO. Look, I’m here to say on Labor Day, that working people, union people are fighting back,” Sen. Elizabeth Warren, D-Mass., said at an event Monday morning. “When unions fight back, all workers get stronger.”

Earlier this month, Trumka would not say a Trump endorsement was out of the question. “I don’t want to see in your story: Trumka says he’ll endorse Trump,” Trumka said, after being asked at a Christian Science Monitor breakfast whether he'd back the president's re-election bid. “I’m not saying that. I’m saying, we’ll consider every candidate who’s running, and our members will help us decide that.”

But he was critical of the overall impact of the president's policies on U.S. workers. “When he does something that’s right for workers, I tell workers around the country that he’s right,” Trumka said. “When he does something that’s bad for workers, I tell them it’s bad. And unfortunately, the number of things we’ve had to oppose is greater than the number of things we’ve been able to support."