A California congressman at the center of a legal battle with the White House on Wednesday asked U.S. trade officials to let him sit in on negotiations in San Diego next week between the United States and other countries in the Asia-Pacific region.

"Given the immense impact that this agreement will have on many areas of the American economy, including intellectual property, I respectfully request that you allow me and certain members of my staff to be present as observers for this round of negotiations," Republican lawmaker Darrell Issa said in a letter to U.S. Trade Representative Ron Kirk.

The unusual request to join the San Diego talks on the proposed Trans-Pacific Partnership (TPP) pact, and a separate letter on Wednesday from about 130 congressional Democrats, reflect the anxiety many lawmakers are feeling about trade agreements, even though Congress last year overwhelmingly approved three such pacts -- with South Korea, Colombia and Panama.

There was no immediate comment from the U.S. Trade Representative's office regarding Issa's request.

The U.S. government is hosting the 13th round of negotiations July 2-10 on the TPP, which would create a regional free trade zone including the United States, Australia, New Zealand, Peru, Chile, Singapore, Malaysia, Vietnam and Brunei.

Those nine countries recently invited Mexico and Canada to join the talks, which are unlikely to reach an agreement before the first part of next year.

The Obama administration describes the TPP as a "21st Century" trade agreement that would set higher standards in areas from workers rights to environmental protection to intellectual property rights, as well as eliminate most, if not all, remaining tariffs between the countries.

Issa, who represents northern San Diego County, is chairman of the House of Representatives Oversight and Government Reform Committee. He has been pushing the White House to release key documents from a botched U.S.-Mexico gun-running scheme.

President Obama has responded by claiming executive privilege to shield some of the "Operation Fast and Furious" documents from congressional investigators.

The roughly 130 Democratic lawmakers, in their letter, urged U.S. Trade Representative Ron Kirk to release draft texts under negotiation and "to engage in broader and deeper consultations" with members of Congress on U.S. laws and regulations they said be could be affected by the pact.

Those include areas such as labor, patent and copyright, land use, food, agriculture, natural resources, the environment, state-owned enterprises, government procurement and regulations for financial services, healthcare, energy and telecommunications, the lawmakers said.

Meanwhile, Senator Sherrod Brown, an Ohio Democrat, on Wednesday introduced a bill that would require the White House to provide Congress with more information about potential free trade partners, including their records on humans rights, labor and the environment, export opportunities and challenges.

"At a time when too many Ohioans are still looking for work, we cannot sign a lopsided trade agreement that tips the balance against American automakers and workers. The rules of trade, and the processes for negotiating the rules matter," said Brown, a staunch opponent of free trade agreements and a spokesman for many union workers who believe the pacts encourage companies to move jobs overseas. (Reporting By Doug Palmer; editing by Gunna Dickson)