Calling NAFTA the "worst trade deal ever made", Trump claimed that the other two countries were being "very difficult.
It was not made entirely clear in the tweet whether he meant he was thinking of terminating talks or terminating NAFTA altogether.
Trump was heavily critical of NAFTA during his campaign trail, and his administration has been in talks to renegotiate the agreement since July, with the aim of reducing the US's trade deficit.
NAFTA took effect in 1994, and is an agreement between Canada, the US and Mexico which aims to eliminate barriers to trade and investment between borders.
In the tweet, Trump threatened to terminate discussions. This is not the first time the President has indicated his willingness to walk away, not just from the talks but from the entire agreement. Earlier week he told a rally of supporters that the US will "end up probably terminating" NAFTA.
The tweet came a few minutes after a restatement of one of Trump's rallying cries, as he called again for a wall to be built along the US Mexico border and to be paid for by Mexico.