President Trump started his Labor Day with an attack on a top union leader, lashing out after criticism from AFL-CIO President Richard Trumka.

Mr. Trump tweeted Monday morning that Trumka "represented his union poorly on television this weekend." He added: "it is easy to see why unions are doing so poorly. A Dem!"

The president's attack came after Trumka appeared on "Fox News Sunday" over the weekend where he said efforts to overhaul the North American Free Trade Agreement should include Canada. Trumka, whose organization is an umbrella group for most unions, said the economies of the United States, Canada and Mexico are "integrated" and "it's pretty hard to see how that would work without having Canada in the deal."

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Mr. Trump is at the White House with no public events scheduled this weekend.

The president said Saturday on Twitter that there was "no political necessity" to keep Canada in NAFTA. But it's questionable whether Mr. Trump can unilaterally exclude Canada from a deal to replace the three-nation NAFTA agreement, without the approval of Congress. Any such move would likely face lengthy legal and congressional challenges. Mr. Trump fumed after the Toronto Star published sentiments he had expressed over the trade talks with Canada, accusing another publication of leaking the remarks.

Trump administration negotiations to keep Canada in the reimagined trade bloc are to resume this week as Washington and Ottawa try to break a deadlock over issues such as Canada's dairy market and U.S. efforts to shield drug companies from generic competition.

Mr. Trump wants to get a trade deal finalized by Dec. 1.

The president said last week that the U.S. and Mexico have come to an understanding on the basics of a trade agreement, and said it wouldn't be called NAFTA, but Mexico continued to use the phrase.

Trumka also said of Mr. Trump: "the things that he's done to hurt workers outpace what he's done to help workers," arguing that Trump has not come through with an infrastructure program and has overturned regulations that "will hurt us on the job."

Asked about the low unemployment rate and economic growth, Trumka said "those are good, but wages have been down since the first of the year. Gas prices have been up since the first of the year. So, overall, workers aren't doing as well."

The national average for gas as of Monday is $2.84 a gallon, according to AAA. Gas prices were closer to $2.50 at the start of the year, according to AAA.

On Monday, the president also touted the economy, saying "Our country is doing better than ever before with unemployment setting record lows." He added, "The Worker in America is doing better than ever before. Celebrate Labor Day!"

The unemployment rate of 3.9 percent is not at the best point ever — it is near the lowest in 18 years.

Mr. Trump has made redoing trade deals and touting the economy key pillars of his presidency, even as other controversies — like a lawsuit against his charitable foundation and convictions of former associates — swirl around him in Washington.