Michigan Rep. Sander Levin, one of the most influential Democrats on trade issues, is stepping up his opposition to the Trans-Pacific Partnership – a trade agreement involving 40 percent of the world’s commerce.

“I have now concluded that the TPP as negotiated is short of an acceptable outcome, and I do not support it,” Representative Levin said Thursday at a Monitor-hosted breakfast for reporters. Levin is the ranking Democrat on the House Ways and Means Committee and a former chairman of the influential panel.

Levin’s opposition will make it harder for the White House to get the TPP deal approved by Congress before President Obama leaves office. The pact covers 12 governments, including Japan and Vietnam.

The trade deal faces an uncertain fate under various potential future presidents. Hillary Clinton, Bernie Sanders, Donald Trump, and Ted Cruz all have stated their opposition to it. Marco Rubio’s campaign says he is “reviewing” his position on the trade pact after previously supporting it.

The agreement was signed Feb. 4 in New Zealand by US Trade Representative Michael Froman. But timing of the White House push for congressional approval remains uncertain. At a White House press briefing earlier this month, press secretary Josh Earnest said, “It’s a complicated process. We are not yet at a place where the president has forwarded the agreement to Congress for their ratification.”

In explaining his opposition, Levin cited several issues including how the lengthy document deals with worker rights, currency manipulation, and rules that determine how much content in a product has to come from a TPP country for it to be subject to lower tariffs.

“Vietnam, Malaysia, and Mexico engage in abhorrent abuses of fundamental rights – competing internationally in a race to the bottom that harms workers everywhere,” Levin said. He added that the agreement is “setting an economic framework for generations. We cannot afford to lock in weak standards, uncompetitive practices, and a system that does not broadly spread the benefits of trade.”

Levin was never an enthusiastic supporter of TPP. He opposed a measure that Congress enacted last year giving the Obama administration the ability to submit trade pacts for a simple up or down vote without the possibility of filibuster or amendment.

"We're disappointed but not surprised given Congressman Levin's votes against trade promotion authority and the trade enforcement bill," said Matthew McAlvanah, assistant US trade representative for public affairs, in an e-mailed statement. "In TPP, we've made historic progress on issues important to House Democrats and look forward to continuing to work on a bipartisan basis to move legislation forward."

At the breakfast, the longtime Michigan congressman was asked how his opposition to the TPP deal differs from that of Mr. Trump, one of the Republican presidential contenders. In an interview with Breitbart News, Trump said, “The deal is insanity,” adding that it “should not be supported and it should not be allowed to happen.”

“He never says what do you do,” Levin said. “You don’t make trade benefit the working families and the economic sector of the United States simply by code words.... I think for Trump it is rhetoric, when what we need with trade is reality.”

Editor's note: This story was updated to include a response from the Office of the US Trade Representative.