The top Mexican trade negotiator said Mexico will walk away from talks to rework NAFTA if the U.S. tries to impose tariffs on Mexican products.

Mexican officials said they do not want the 23-year-old deal to fall apart, but they are unwilling to discuss the types of tariffs called for by President Donald Trump, Bloomberg reports. In January, White House Press Secretary Sean Spicer suggested a 20% tariff on Mexican goods could pay for Trump’s border wall.

Officials said the talks are set to start in June. Mexican officials said they do not think it would be a total crisis should talks fail, considering the U.S. can only impose an average 3% tariff on Mexican goods under World Trade Organization rules. Those rules would kick into effect without NAFTA — as long as the U.S. remains a member of the WTO and follows the rules.