Defying bank and congressional critics, the National Credit Union Administration on Thursday approved a new rule that will substantially expand credit union eligibility and size.

In a 2-to-1 vote, the NCUA board gave in to credit union demands and expanded the list of people who can join a credit union by virtue of their relationship to an existing or potential member.

Effective Jan. 1, unmarried gay and straight couples, roommates, live-in nurses and maids, and other unrelated people who live together can join one another's credit unions, provided they share rent or otherwise act as an economic unit.

Perhaps more importantly, credit unions will be able to add new groups to their membership for the first time since Oct. 23, 1996, when a federal judge in the AT&T Family Federal Credit Union case temporarily prohibited such growth.

The NCUA also decided to give expedited consideration to community-based credit unions that seek to serve a single county of 300,000 or fewer people. Larger communities would also be considered but under a tougher standard.

Bankers were livid, if not surprised.

"It's pretty much what we expected," said Beth L. Climo, director of financial industry affairs at the American Bankers Association, which was a plaintiff in the AT&T case. "The rule NCUA adopted today snubs congressional intent."

Among other things, the ABA had argued that the population ceiling for community-based credit unions should be set at 25,000.

Ms. Climo also criticized the NCUA's decision to set a soft floor of 3,000 potential members for new credit unions. "Their rule presumes that if your group has fewer than 3,000 potential members, it's not economically viable," she said. She said the rule will drive some small groups to join existing credit unions.

Interestingly, NCUA Chairman Norman E. D'Amours made the same complaint in explaining why he voted against the rule.

Thad Woodard, president of the North Carolina Bankers Association, predicted the new rule would anger small credit unions and bolster the case for taxing large ones.

He mocked the NCUA's decision to let unrelated household members join credit unions, saying it would qualify virtually every American. "They may leave out that branch of man that is still swinging in the trees, but that's about it," he said.

Both Ms. Climo and Mr. Woodard raised the possibility of suing to stop the NCUA. They said the ABA's credit union task force will meet shortly to discuss litigation and other options.

Though most of the NCUA's rule automatically goes into effect Jan. 1, Congress has 60 days to challenge two provisions in the NCUA's implementing rule: the definition of eligible family and household member, and the definition of "reasonable proximity"-the acceptable distance between an existing credit union and new groups that it wishes to add to its membership. The NCUA did not define the term and said it will judge "reasonable proximity" on a case-by-case basis.

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