The Mexican peso fell against the U.S. dollar on Monday after voters in the second-largest Latin American economy overwhelmingly voted in favor of a far-left candidate as its new president.

The peso pulled back 0.6 percent versus the dollar, erasing slight gains seen on Sunday, to trade at 20.032.

Andres Manuel Lopez Obrador, better known by his initials AMLO, received more than 50 percent of the vote in an election held Sunday. His two closest rivals only got about 23 percent and 15 percent of the vote respectively.

His victory, however, could lead to tougher negotiations between Mexico, the U.S. and Canada on a new NAFTA deal at a time when trade relations between the three countries are rising.

“In many ways, it’s going back to the era before NAFTA in Mexico,” Carlos Gutierrez, former U.S. Commerce secretary, told CNBC’s “Squawk Box” on Monday. “I don’t think he’s going to make the negotiations any easier because a lot of what he would like to do will bump up against NAFTA.”

“This is not a good event here,” Gutierrez said. “He’s not going to back away from his instincts, and his instincts are left-wing, populist, anti-multinational (companies), nationalist.”