WASHINGTON — Japanese Prime Minister Shinzo Abe on Friday formally requested Japan’s inclusion in the ongoing Trans-Pacific Partnership negotiations between the U.S. and 10 other countries.

Adding the world’s third-largest economy to the negotiations could potentially provide new opportunities for U.S. apparel, textile and footwear exporters, but it also brings a new level of complexity to the talks, which some fear will impede the goal of reaching a final trade accord this year.

While the news was welcomed by the U.S. Trade Representative’s office, it joined many business groups and lawmakers in voicing concern about including Japan in the talks, which seek to create an Asia-Pacific regional trade agreement.

“Since early last year, the United States has been engaged with Japan in bilateral TPP consultations on issues of concern with respect to the automotive and insurance sectors and other nontariff measures, and also conducting work regarding meeting TPP’s high standards,” said Demetrios Marantis, who was appointed acting USTR on Thursday, succeeding Ron Kirk. “While we continue to make progress in these consultations, important work remains to be done. We look forward to continuing these consultations with Japan as the 11 TPP countries consider Japan’s candidacy for this vital initiative in the Asia-Pacific region.”

The U.S. and TPP partners Vietnam, Australia, Brunei, Chile, Malaysia, New Zealand, Peru, Singapore, Mexico and Canada must formally approve and invite Japan to join the talks. If approved, USTR must notify Congress, which triggers a 90-day consultation period on U.S. negotiating objectives relating to Japan. Several lawmakers have voiced concern about allowing Japan into the talks, arguing in a letter to Obama that the country’s market has been “impenetrable” to U.S. auto exports because of high trade barriers.