Under the CECL standard, institutions will have to recognize the expected lifetime losses at the time a loan or financial instrument is recorded.

The standard does not become effective for credit union Call Reports until the start of 2022.

"While this may appear to some to be far off, when you consider the amount of work required to adopt necessary changes—even if using a vendor—it is much closer than many credit unions may realize," Nussle wrote.

Credit unions have argued that they should not have to comply with the standard.

"NAFCU maintains that credit unions should never have been included within the scope of the CECL standard because they were not part of the poor lending practices that precipitated the financial crisis," NAFCU President/CEO B. Dan Berger said in a letter last year to the House Financial Institutions and Consumer Credit Subcommittee.

Nussle echoed those sentiments in his own letter to the subcommittee.

In a letter to credit unions outlining the agency's supervisory priorities earlier this year, McWatters said that requirements for CECL will continue to "evolve."

He said, however, that examiners will inquire this year about how credit unions are preparing for the new accounting standard.

Nussle said that in February 2018, the FDIC and the Federal Reserve Board hosted a webinar on CECL, adding that the session was well received by those participating.

He said that NCUA should consider using that webinar as a model, saying that some credit unions are not yet focused on the issue.

"Some have not yet elevated CECL preparation to a top priority simply because of a lack of information and understanding of how the standard will change current practices and how to begin implementing necessary changes," he told McWatters.