Sen. Rob Portman (R-OH) speaks during the Republican Jewish Coalition Spring Leadership Meeting in Las Vegas, Nevada April 25, 2015. REUTERS/David Becker

WASHINGTON (Reuters) - Republican U.S. Senator Rob Portman on Thursday said he opposes the Trans-Pacific Partnership trade deal in its present form, dealing a significant blow to the pact a day after officials from 12 countries signed it.

Portman, from Ohio, said the Pacific trade deal fails to meet the needs of his state’s workers because it lacks an enforceable provision to fight currency manipulation and because of new, less-stringent country-of-origin rules for auto parts.

“I cannot support the TPP in its current form because it doesn’t provide that level playing field,” Portman said in a statement.

While approval of the trade pact is a top priority of President Barack Obama this year, his final year in office, it faces stiff opposition from many of his fellow Democrats in Congress.

Meanwhile, Republicans have begun voicing concerns with specific provisions and are indicating that they are in no rush to bring the deal to a vote.

Besides insisting that portions of the sweeping pact be renegotiated, some Republicans worry that bringing TPP to a vote before the November elections could hurt the chances of some of their incumbents running in swing states or congressional districts.

Portman is seeking a second term in an industrial state where many workers blame job losses on previous trade deals such as the North American Free Trade Agreement (NAFTA). He is expected to face a stiff challenge from former Democratic Governor Ted Strickland.

The 12-nation deal would liberalize trade from Chile to Japan, representing 40 percent of the world economy.