WASHINGTON — 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 in seven years to hit the picket line at a major U.S. airline.

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 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 that 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 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. AMFA also incensed the pilots’ union by refusing to take cuts after pilots accepted concessions. Only flight attendants voted on whether to strike with AMFA — and they rejected it.

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. That leaves Northwest Airlines with little resistance and what probably will be a relatively easy time ridding itself of workers represented by AMFA, analysts say.

“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.”