A $7 billion-asset Warrenville credit union that suffered massive losses in mortgage-backed securities was one of three critically undercapitalized institutions seized Friday by the U.S. government.

Members United Corporate Federal Credit Union was one of three “wholesale,” or “corporate,” credit unions put into conservatorship by the National Credit Union Administration.

Such credit unions act like banks and provide various services for the nation’s 7,500 retail or consumer credit unions, which serve about 90 million consumers.

“This will be invisible to the consumer,” NCUA Chairman Debbie Matz said in a late afternoon conference call with reporters. They’ll never even be aware this has transpired.”

Charles Furbee, a former Federal Reserve Bank of Chicago official, has been named interim chief executive of Members United, the NCUA said.

The other two corporate credit unions seized Friday were headquartered in Texas and Connecticut. The trio had total assets of more than $15 billion.

Two other corporate credit unions were seized last year.

The credit union industry, not taxpayers, will bear the cost, estimated at more than $7 billion, of the conservatorships.

“For the last two years corporate credit unions have been seriously affected by the economic downturn,” Matz said. “For the most part this resulted from an overconcentration in mortgage-backed securities, which left five corporate credit unions with severely impaired balance sheets.”

Speaking specifically about Members United, she said their securities were Triple A when they were originally bought.

But “when the markets collapsed, their portfolio took a serious hit, and because they were so over-concentrated, they were not able to recover,” Matz said. “We’ve determined that they’ll never be able to become a viable institution again.”

Matz stressed that no consumer transactions have been or will be interrupted, and no credit union members have lost a penny of insured funds. Deposits will continue to be covered up to $250,000 per account.

The seized credit unions’ bad securities will be bundled and sold to investors.

About 70 percent of the assets of corporate credit unions are now under conservatorship.

But Matz said retail credit unions “have come through this economic storm quite well.”

As a group, “they’re well capitalized,” she said, while noting that certain individual retail credit unions are having problems.