If credit unions were subject to income taxes, they would lose a key part of what makes them unique, but experts are divided as to whether it would create a stampede of bank conversions.

"Being taxed would cause a real difficult adjustment for some credit unions. They'd have to increase efficiencies, at the very least. But it is not at all clear that they would conclude that changing over to a bank would be better for their members," said Janice Hollar, a former credit union CEO who is now senior vice president of RP Financial LC. The Virginia-based consulting firm works with banks and credit unions on strategic planning, mergers and business plans.

"A credit union that is happy with the services it offers its members would have less incentive to switch. The biggest factor in deciding on a conversion would be how the credit union's business model has matured," she added.