America's powerful UAW labour body has launched a blistering attack on proposals for Japan to enter the Trans-Pacific Partnership (TPP), claiming the move would cost "tens of thousands of jobs."

The possibility of Japan entering the TPP has been welcomed by the Global Automakers Association, which maintains the inclusion of all major, automotive countries on the Pacific rim would create a single set of consistent rules and increase trade, but the UAW is taking a radically different view.

"The UAW strongly opposes Japan's entry into the Trans-Pacific Partnership (TPP) because their inclusion would undermine our nation's ongoing economic recovery," said a UAW statement.

"Japan's inclusion in the TPP would cost the loss of tens of thousands of automotive manufacturing jobs in the US because of long-standing closed markets. Although Japan's trading partners have worked for decades to open the Japanese market to imported automobiles, Japan remains the most closed automotive market in the world.

"Despite a Japanese automotive import tariff that is already at 0%, global import penetration remains less than 6%."

The UAW also claims there is an "enormous trade deficit" in the automotive sector, insisting for every 117 Japanese cars sold in the US, just one American vehicle is bought in Japan.

"The UAW commends President Obama for his leadership and support for the US auto industry," added the UAW. "Domestic automakers have pledged to make investments that will mean more than 40,000 direct manufacturing jobs in the US through 2015.

"President Obama's actions helped prevent a second great depression, and he saved more than a million American jobs. We must build on this success and not allow it to be jeopardised by enacting a trade deal that only benefits Japan."

The Association of Global Automakers has encouraged broad possible participation in the TPP, including that of Canada, Mexico, and Japan.