Washington — U.S. President George W. Bush, who has courted several conservative-leaning unions since taking office almost two years ago, wielded what organized labour considers a decidedly anti-union weapon when he intervened to stop a West Coast port labour dispute.

Mr. Bush was the first president in a quarter century to invoke the emergency provisions of the Taft-Hartley Act of 1947 when he asked a federal court to reopen the 29 ports and impose an 80-day truce between dockworkers and shipping companies.

Mr. Bush said the 10-day lockout was a threat to the nation's economy and security, and his request was approved by a federal judge in San Francisco on Tuesday.

Still, White House officials fretted about the impact Mr. Bush's move would have on the fragile relationship he slowly has been building with some unions, including the Teamsters and the United Brotherhood of Carpenters. Officials tried to soothe concerns of those unions and asked for political mercy in the criticism that would follow.

Democratic candidates depend on heavy turnout from union workers. Just four weeks before midterm elections, Mr. Bush's advisers, who have been working to divide labor, also worried his intervention would instead drive angry union voters to the polls.

"It is a tragedy with historic ramifications," said Richard Trumka, secretary-treasurer of the AFL-CIO, a federation of 65 member unions.

But Republican allies dismissed concerns of a political fallout.

"Frankly, are people really going to go to the polls and pull the lever based on how this dispute played out? I don't think so," said Pat Cleary, vice-president for human resources policy at the National Association of Manufacturers. "It will have no effect."

Union leaders whom Mr. Bush has been courting, such as Teamsters president James Hoffa and Carpenters president Doug McCarron, care more about jobs than the labour law, Mr. Cleary said, adding that just 10,500 dockworkers were affected by Mr. Bush's decision.

Mr. Bush also could reap benefits. White House advisers welcomed the chance to head off a burgeoning crisis and perhaps ease concerns about his handling of the economy. Polls show a growing number of voters want Mr. Bush to spend more time talking about the economy than Iraq. His economic programs have either stalled in the Senate or have failed to jump start the economy.

Mr. Bush was gambling that, this close to the elections deciding control of Congress, his intervention in the dockworkers' labour dispute would do more to demonstrate his care about the economy than stoke a labour-driven voter backlash on Nov. 5.

"I'm going to work as hard as I possibly can to do everything we can do to make sure our economy grows," Mr. Bush told a Tennessee audience in advance of the announcement he was seeking the court injunction.

But union leaders say Mr. Bush has gone too far. They consider Taft-Hartley an anti-union mechanism that is used to give management the upper hand in disputes.

"This is the first time in the history of the United States that a president has let an employer lock out workers in an extended quest to undermine the workers' union, creating a phony crisis and then reward that employer's action with government intervention," Mr. Trumka said.

Add Tuesday's Taft-Hartley move to Mr. Bush's effort to strip some union rights and civil service protections from federal workers in the new Homeland Security Department and the push by his administration that led to congressional repeal of work safety regulations, and that's enough to energize union voters on Nov. 5, labor leaders say.

Mr. Bush's advisers denied his actions were an attempt to bust unions. "If what they wanted to do was go back to work, then this is good," Commerce Secretary Donald Evans said. "The President is making it so they can go back to work while working out their differences."

Taft-Hartley has severely limited the power of unions by instituting controls and deterrents, labor experts say. The law takes away unions' most stringent weapon in negotiations — the right to withhold labor.

During the Great Depression, labour won sympathy from the public, which led to the National Labor Relations Act that ensured workers' rights to organize and bargain collectively. But political and public unrest after the Second World War curbed those rights with Taft-Hartley. Some activists blame it for contributing to labour's decline in membership, now just 13.5 percent of the work force.

Court-ordered cooling-off periods also tend to lower "public support for unions by portraying them as selfish economic actors who harmed the nation," said Michael LeRoy, labour professor at the University of Illinois at Urbana-Champaign.