Fox, who was Mexico's president from 2000 to 2006, is one of the commander in chief's most outspoken critics. He's been particularly vocal about plans for a wall along the U.S.-Mexico border.
This time, though, it appears the president's vacation has hit a nerve with him.
Fox took aim at the president's 17-day vacation, which he kicked off Friday at Trump National Golf Club in Bedminster, New Jersey.
".@ RealDonaldTrump leaving on vacation, huh? What for? If you're not happy with your job, just leave. After all, it was never for you."
Fox was not alone, though, of his criticism of the president. The twittersphere lit up Friday with his foes slamming him for the length of the vacation.
Earlier in the day, Fox also mocked Trump for claiming that he is responsible for a growing economy. Fox tweeted an article claiming former President Barack Obama is responsible, adding, "See that, @realDonaldTrump , you've achieved nothing. You brag the results of others."
And earlier this week Fox wrote a tweet laced with profanity to express his opposition to a border wall.
"@RealDonaldTrump, once again I tell you: we're not paying for the # F---ing Wall ! Do not try to use us for your own good."