President Donald Trump on Monday started the process of officially pulling the United States out of the landmark Paris Climate Agreement. His administration cited an excessively high cost for American taxpayers and businesses.

“President Trump made the decision to withdraw from the Paris Agreement because of the unfair economic burden imposed on American workers, businesses, and taxpayers by U.S. pledges made under the Agreement,” Secretary of State Mike Pompeo said in a statement. “The United States has reduced all types of emissions, even as we grow our economy and ensure our citizens’ access to affordable energy.”

Pompeo added that “innovation and open markets” would help spur lower emissions.

Trump’s announcement formalizes a pledge he made two years ago. Since the withdrawal process takes one year, the U.S. will officially exit the accord after the 2020 election. The process starts with a letter to the United Nations. However, it’s important to note that the conditions of the Paris deal state no nation can pull out of the agreement in the first three years.

The Paris Climate Accord is a deal signed by nearly 200 countries that each set their individual goals for curbing greenhouse gas emissions and other forms of pollution. It was devised in 2015 and went into effect in November 2016. As part of the deal, the U.S. had agreed to reduce emissions roughly 28% under 2005 levels by 2025.

SLIDESHOW: TOP DEMOCRATS RUNNING FOR PRESIDENT IN 2020

Several 2020 Democratic presidential candidates have said that within their first 100 days in office, they would promise to recommit the U.S. to the Paris Climate Accord. Several of the contenders, as well as environmental groups, rebuked the Trump administration’s decision.