WASHINGTON - Democrats in Congress who backed legislation key to sealing a Pacific Rim trade pact this week have shrugged off threats of retribution from labour unions and liberal activists who vowed to hold them accountable at the polls.

Forty-one Democrats defied pressure and supported legislation to let the White House seal trade deals and fast-track them through Congress.

Unions and political groups such as Democracy for America and the Working Families Party have pledged to hold pro-trade Democrats' feet to the fire, including potentially running rival candidates at primaries for 2016 congressional elections. Working Families said discussions were under way about possible House challenges.

Lawmakers, who have endured picketing, protests, sit-ins and advertising campaigns during a bruising battle for congressional approval, were largely unfazed.

"One doesn't like to have your friends cranky but I've been serving this community for decades," said Oregon Representative Earl Blumenauer.

"If they oppose me because of trade I think it helps me politically, quite frankly," said first-term Representative Brad Ashford of Nebraska. "We have strong labour unions and they are my friends, but if they choose to oppose me because of a Bill that will actually provide bigger and better and higher-wage jobs for them, that's their choice."

Democrats who voted for Trade Promotion Authority may also win backing from business groups more commonly aligned with Republican candidates, such as the US Chamber of Commerce and the National Association of Manufacturers.

Trade supporters have a promise from President Barack Obama that the White House would have their backs if they were challenged by unions.

REUTERS