In a world known for solidarity and brotherhood, the Aircraft Mechanics Fraternal Association stands almost alone among labor unions, even as 4,400 of its members walk the picket line.

The Northwest Airlines Corp. mechanics and cleaners who went on strike Saturday are the first workers at a major U.S. airline to hit the picket line in seven years. But, despite major upheaval in the industry where many pilots, flight attendants and other workers have had to make concessions in pay and benefits, the striking workers are finding little support from other unions.

AMFA, which grew in recent years by winning members away from other unions, is an outsider in the labor movement. "They are a go-it-alone union. They are proud of that," said Richard Bank, director of collective bargaining with the AFL-CIO. "They made their living raiding AFL-CIO affiliates with that message. So it's rather surprising to see them now calling for solidarity with their cause."

But what happens to AMFA and its Northwest mechanics could have a broad impact on organized labor and the airline industry, well beyond Northwest Airlines, according to labor experts.

"This is a perfect target for Northwest," said Charles B. Craver, a professor of labor law at George Washington University. "It's a union that is sort of weak. It's not AFL-CIO. If this were [the AFL-CIO's International Association of Machinists and Aerospace Workers], Northwest might be a little more nervous."

The airline's other employees have continued working during the strike. In contrast, nearly 1,000 baggage handlers, counter agents and other employees walked off the job earlier this month in sympathy when employees with a British Airways caterer were fired, causing the airline to cancel hundreds of flights.

Other industries, struggling to deal with their own labor costs, will be watching the strike closely. Northwest said it needs to cut labor costs by $1.1 billion, and its pilots have agreed to a 15 percent pay cut. AMFA said the airline is seeking to cut its mechanic workforce in half and cut the remaining workers' pay by 25 percent.

Since its inception, AMFA has been perceived as an upstart by the AFL-CIO. It was "more of a rogue union that came in and took advantage of a period of high grievances with machinists and promised these guys the world," said Robert A. Bruno, professor of labor at the University of Illinois at Urbana-Champaign. AMFA's big break came in 1999 when the mechanics at Northwest decided to decertify the machinists union and move to AMFA instead.

That created a major rift with the AFL-CIO and its member unions, which accuse AMFA of stealing members. The discord remains between the AFL-CIO and AMFA and between AMFA and the unions that recently split from the AFL-CIO. That leaves the union largely on its own during its biggest fight yet.

The relatively small union was founded in 1962 to represent only skilled mechanics. Then in 1999, it pulled Northwest's mechanics away from the International Association of Machinists and Aerospace Workers. In 2003, United Airlines' mechanics also left the IAM and joined AMFA after the IAM agreed to a 13 percent wage cut.

AMFA has about 17,000 members, compared with the IAM's approximately 100,000.

That pattern of "raiding" has isolated AMFA from other, more established unions, which refuse to respond to the strike. That leaves Northwest Airlines with little resistance and what will probably be a relatively easy time ridding itself of workers represented by AMFA.

"I think the mechanics have shown a lot of courage but not much longer-term strategy here," said Harley Shaiken, a labor professor at the University of California at Berkeley. "The kind of outreach that is necessary to have a much broader base, they really didn't do."

As it became clear AMFA might strike, it asked other unions for support -- with little success. The IAM's general vice president, Robert Roach Jr., wrote AMFA's leader, O.V. Delle-Femine, saying, "It is about time that AMFA recognizes that it cannot win a major labor dispute standing in isolation." He went on: "IAM members will not be duped into standing with AMFA. AMFA has never honored an IAM picket line."

AMFA received similar cold responses from other unions.

However, the union and its strikers are receiving other kinds of support, said Steve MacFarlane, AMFA spokesman. "We're getting a tremendous amount of help from all the other unions individually. We're getting all kinds of information from our fellow workers" who remain on the job, he said. "We never expected the others to honor our picket line, but of course we would have welcomed that," he said. "But we never calculated that as a part of our strategy."

The International Longshore and Warehouse Union has spoken out in support of AMFA. "I ask all ILWU members to do everything in their power to help these workers in the struggle as if it were your own," James Spinosa, international president, said in a letter to the union's locals.

The employees and staff of the International Brotherhood of Teamsters will not be flying Northwest Airlines. But the group is not organizing a formal boycott, and its members are making their own decisions about how they will respond, said Leigh Strope, a Teamsters spokeswoman. Not flying Northwest is "a show of respect for the workers at Northwest Airlines rather than a sign of support for AMFA," she said Friday in an e-mailed statement.

In the long run, the lack of support for AMFA may have more of an effect than unions anticipate, according to some labor watchers.

"If the workers don't stand together, Northwest may be able to destroy this union because it is not a big union. It may then go on to the flight attendants and baggage handlers," Craver said. "And if they are able to get away with it, it will embolden all the airlines. And worse yet, it will spread to other unions in other industry where they demand huge concessions or else."

Northwest Airlines striking mechanics picket at the airport in Detroit, one of the airline's hubs. None of the airline's other employee groups have walked off the job.Replacement mechanics work on the main landing gear of jet at Detroit's airport. The AMFA pulled Northwest mechanics away from an AFL-CIO union in 1999.