The proposal would create inconsistent supervision of financial institutions solely based on charter type, she wrote.

"To ensure safety and soundness of commercial real estate assets, we strongly implore NCUA to adopt standards that are consistent and align with the rest of the financially regulated institutions as members of the [Federal Financial Institutions Examination Council]," she added.

In its proposal, NCUA officials said they had consulted with the other banking regulators as the agency developed its proposal.

While credit union trade groups had some concerns about the proposed appraisal rule, they were pleased with the threshold increase.

If the threshold is increased, credit unions will be able to use their judgement in deciding when, and if, appraisals are needed for commercial property that falls under the $1 million threshold, Luke Martone, senior director of advocacy and council at CUNA.

"In supporting the proposed threshold increase, we agree with NCUA that statutory limits, combined with appropriate prudential and supervisory oversight, should sufficiently offset any potential risk that could occur by raising the appraisal threshold for nonresidential real estate-related transactions," Martone wrote in a reaction to the NCUA proposal.

Andrew Morris, NAFCU's senior council for research and policy agree.

And he added, "as the NCUA's experience and material loss reviews indicate, faulty appraisals were not the cause of credit unions' loss experience during the financial crisis."