The NCUA liquidated Melrose, located in Briarwood, N.Y,,  Friday after the New York credit union lost $744.6 million over the past three years as its taxi medallion loans soured. The Teachers Federal Credit Union of Hauppauge, N.Y. assumed all of Melrose's members and shares, as well as some loans and other assets.

But a Teachers spokesman said the credit union did not accept any loans based on taxi medallions. For many years those medallions were valuable assets, but their value has dropped as the popularity of ride-sharing services has increased.

"Up until five or six years ago those taxi medallion loans were some of the best collateralized in the country," Dollar said.

"To blame NCUA for not having a crystal ball twenty years ago to foresee the uber-fication of the taxi business and to make those credit unions write down their medallion loans in advance for something totally unforeseeable is just not a fair criticism of the agency, in my view," he said.

He added that once the value of the medallions plunged, the NCUA anticipated the problem by increasing the agency's operating equity level to handle any losses.

NCUA board member Rick Metsger has said that Congress pushed the agency to make loans such as those based on taxi medallions.

"Most credit unions cannot put more than 12.25 percent of their assets into member business lending," Metsger said, in a December speech "but the taxi medallion credit unions were able to put up 100 percent of their assets."

The Credit Union Membership Access Act of 1998 specifically address such loans.

The law placed some limits on business lending. However, the conference report for the bill also states, "This title provides exceptions for insured credit unions that are chartered for, or that have a history of primarily making member business loans to their members, such as members who are of a specialized vocation, for example: fishermen, farmers, truck drivers and taxi cab drivers."

The NCUA, however, has warned credit unions about having too much concentration in a single product.

"It is up to credit union management to identify the risk in each product or service line, quantify the risk and set appropriate concentration limits based on the analysis," the agency said, in a 2010 letter to credit unions.

And in a 2014 letter to field staff, Larry Fazio director of the agency's Office of Examination & Insurance, specifically addressed taxi medallion loans.

"While recent history reflects a continuously rising market price for medallions, an adverse change in market conditions and economic cycles can decrease prices," he wrote.

He added, "A credit union with a large concentration of taxi medallion loans must have documented policies and practices in place that ensure concentration risk is appropriate for their net worth levels and consistent with the credit union's strategic plan."