National union leaders urged their members to call their elected officials Wednesday in another attempt to defeat a pending international trade deal.

The Trans-Pacific Partnership (TPP) has faced opposition from unions who claim it would be harmful to workers. President Barack Obama found himself at odds with many within his own party for negotiating the deal. Labor unions renewed their opposition in the hopes lawmakers will reject it.

“Civil society groups all over the country are calling on Congress,” the Teamsters said in an email to members, which was obtained by InsideSources. “We urge Teamsters everywhere to join this action and flood Congress’s phone lines today with calls to every lawmaker asking them to pledge their opposition to the TPP.”

The president has begun renewing efforts to win enough support in Congress. The trade deal has sat without a vote since being finalized October 2015 by the partner countries. Labor unions claim the deal would undermine worker rights while benefiting large international corporations.

“Multinational corporations and Republican congressional leaders want to jam through the TPP,” the United Auto Workers said in a message to members. “[It’s] an awful trade deal that will put Americans out of work, degrade environmental protections and increase prescription drug price.”

The trade deal is designed to gradually end thousands of import tariffs and other international trade barriers. It would also establish uniform rules for intellectual property, environmental protections and open Internet access. The trade deal is likely to have a significant impact on international trade at roughly 39 percent of global GDP.

The White House has argued the trade deal will actually help workers despite what unions claim. It will cover a few countries known for notorious labor violations. Communist Vietnam, Malaysia and Brunei are among the partner countries cited for labor and human rights violations.

Unions and other critics have compared the deal to the North American Free Trade Agreement (NAFTA). They claim the deal resulted in many American jobs being lost. The president has previously insisted the deal could help fix many of the problems NAFTA caused.

Labor unions have tried numerous methods to fight the trade deal. They have held rallies and launched media campaigns, including attacks on liberals. Democratic Rep. Kathleen Rice was the target of a video in June 2015 for breaking with unions to support fast-tracking the trade deal.