A number of US politicians are voicing concerns that ongoing Trans-Pacific Partnership (TPP) talks are failing to address concerns over currency disciplines.

Six Republican and Democrat politicians – four members of the House of Representatives and two senators – led by Mike Michaud and Lindsey Graham, have written to President Obama to outline their worries.

“A well-negotiated TPP has the potential to help American businesses and workers, but an agreement that fails to address foreign currency manipulation could further harm the United States economy by leading to a permanent unfair trade relationship,” they said.

The letter follows two bipartisan letters written last year and signed by 230 members of the House and 60 senators asking the administration to address currency manipulation in the TPP negotiations.

To date, there has been no response from the administration, the politicians say.

“Congress ratifies free trade agreements, and we expect our concerns to be addressed in a strong and effective manner,” the letter continues.

“Thus far, United States trade negotiators have failed to propose currency disciplines in any TPP negotiating rounds, and our written concerns have gone unanswered.”

The 12 nations involved in the talks are: Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the US and Vietnam.