The Mexican peso fell to its weakest level in over two months against the U.S. dollar on Friday after a surprise announcement by President Donald Trump to impose tariffs on that country in retaliation over a heavy flow of migrants across the border. The peso USDMXN, -0.19% slid to 19.638, a drop of 2.6% on the session and level not seen since roughly March, according to Factset Research. In a tweet late Thursday, Trump said the U.S. would impose a 5% tariff on all Mexico imports until that country stops the flow of illegal immigrants into the country. He said the tariffs will rise to 10% on July 1 if the crisis persists, and by another 5% for every successive month, up to 25% by Oct. 1. The news drove investors to the Japanese yen, a haven asset in times of economic and geopolitical worries, with the U.S. dollar USDJPY, +0.02% falling to 108.90 yen, a drop of 0.6% on the session. The ICE Dollar Index DXY, -0.01% eased 0.05% to 98.091.