The Oklahoma City-based Tinker Federal Credit Union, which has $3.4 billion in assets and 319,000 members, warned in its comment letter that it would have to rethink a big part of its business model if the rules take effect.

"Should this proposed rule be implemented, 17.37% of TFCU's workforce would become eligible for overtime by shifting them from exempt to non-exempt," Senior Vice President of Human Resources Susan Rogers wrote. "Assuming we maintained their full-time status, merely projecting each of those newly overtime eligible employees worked five hours overtime per pay period (130 hours annually) the credit union's labor expenses would increase 67.8% in 2016 alone."

Rogers said the credit union would end up paying almost 70% of its employees overtime.

"We may have to shift full-time allocations to part-time allocations in order to manage labor costs," Rogers added. "If we were to change the number of full-time allocations, we would have some employees who would no longer be eligible for health benefits. Although every effort would be taken to manage this type of reorganization through attrition, a reduction in work force would be considered."

The Manhattan Beach, Calif.-based Kinecta Credit Union, which has $3.8 billion in assets and 278,000 members, voiced similar concerns.

"The projected additional payroll expense would be far from immaterial, and our business like many others cannot just absorb it and move on," President/CEO Keith Sultemeier told the DOL. "Many of our management positions require short periods of intensive work (e.g., closing the books at month end), and then experience a lull thereafter. These employees work more hours in peak times and less in others. Our employees understand that this is the nature of their jobs and that we will ensure their life balance can be maintained. This is not a broken system, and the proposed dramatic disruption of it is unnecessary."

Because the credit union "cannot expect an increase in revenue or productivity to magically appear" after adopting the rule, the likely response will be payroll cuts and/or reduced wages for nonexempt employees, Sultemeier said.

According to Ellen Davis, assistant vice president of human resources at the Fremont, Mich.-based Gerber Federal Credit Union, there could be fewer promotions, too.

"I foresee that the proposed rule will provide fewer opportunities for advancement because employers will not be able to pay the higher wage," Davis said. "It will no longer set apart middle managers from workers entitled to overtime pay, because the cost of hiring employees at the middle management level will be unaffordable to many small employers. This will result in significant limitations on the upward mobility of the very population that our government should be encouraging to progress and advance."

Missouri Credit Union Association President Don Cohenour added, "Setting one salary threshold for the entire country overlooks the fact that the cost of living throughout the country varies and salaries in different regions vary to reflect that."

Approximately 35% of all credit unions in the United States have no employees that make more than $50,000, Cohenour said. And according to Wisconsin Credit Union League Regulatory Counsel Paul Guttormsson, among credit unions with less than $10 million in assets, almost all CEOs make less than $50,000. Among those with $10 to $20 million in assets, roughly half of CEOs make less than $50,000.