The euro fell to a three-week low on Monday while the Mexican peso also came under pressure after President Donald Trump threatened to impose a 30% tariff on imports from two of the largest U.S. trading partners beginning August 1.

President Trump is threatening the European Union and Mexico with 30% tariffs. The EU warns of counter measures if the tariffs kick in on Aug. 1.

President Donald Trump posted letters to the leaders of Mexico and the European Union, saying they had not done enough to head off the new tariffs.

S&P 500 futures lost 0.5%, while Nasdaq 100 futures dropped 0.6%. Futures for the Dow Jones Industrial Average fell 204 points, or 0.5%.

If he moves forward with the tariffs, it could have ramifications for nearly every aspect of the global economy.

If a 30 percent tariff on Mexico goes into affect on August 1, a wide variety of foods will be more expensive, experts warn.

July 13 (Reuters) - German Finance Minister Lars Klingbeil said on Sunday the European Union must take "decisive" measures against the United States if tariff negotiations fail to cool an escalating global trade war. Get a look at the day ahead in European and global markets with the Morning Bid Europe newsletter. Sign up here.

European Union President Ursula von der Leyen says the bloc will extend its halt on imposing tariff countermeasures while it continues to seek a negotiated trade agreement with the Trump administration.

President Donald Trump released two tariff letters on Saturday, imposing duties of 30% on products from Mexico and the European Union.

The European Commission responded to Trump's announcement in a written statement, saying it remains ready to reach an agreement, while also taking "necessary steps to safeguard EU interests, including the adoption of proportionate countermeasures.