In states where recreational use is legal, sales of marijuana is or soon will be controlled by the states' liquor control boards. Both Colorado and Washington currently permit cannabis sales in various forms, and Alaska and Oregon will likely follow suit early next year.

However, with the exception of Washington, credit unions and banks in the other states have not rushed to fill the service gap. This has led to McWatters' cash-on-the-street concerns, as well situations in which proceeds from marijuana sales are finding their way into the financial services through some questionable methods.

“I have been told in no uncertain terms that cannabis cash is working its way into the financial services system through deposits made by dummy corporations,” McWatters said. “This a situation that causes concern both for NCUA and the FDIC because it raises Bank Secrecy Act questions.”

Credit unions and banks have been issued clear guidance for serving cannabis businesses by the Financial Crimes Enforcement Network (FinCEN) and the Cole memo, issued by former U.S. Department of Justice Deputy Attorney General James M. Cole on April 29, 2013. The memo offered specific directions to federal prosecutors concerning marijuana law enforcement in all U.S. states and serves as guidelines for financial institutions that serve these businesses.

Read more: Complying with the Cole memo will be costly for state regulators and financial institutions …

However, compliance with the Cole memo and other state and federal requirements mans significant and sometimes costly due diligence both by state regulating bodies and any financial institutions that work with cannabis enterprises. In addition, Monday's appointment of U.S. attorney general Loretta Lynch, who holds a much stronger anti-marijuana stance than her predecessor Eric Holder, may change the federal government's tolerance levels for casual marijuana use.

For credit unions considering serving marijuana-related businesses, it generally comes down to a cost-benefit analysis, McWatters said. Lack of critical mass when it comes to both the number and size of the marijuana businesses served may make service too costly, rendering the question moot for many credit unions.

“If you have a credit union with a substantial part of this business, you can probably afford to hire the lawyers and accountants to comply with the Cole memo and still sleep well at night with the comfort that you won't be indicted,” McWatters said.

The NCUA's role in these cases is to continue serving as gatekeepers to make sure that all appropriate federal laws have been observed and credit unions, whether they serve marijuana-related businesses or not, are operating in a safe, sound manner, McWatters said. To date, the board member has heard nothing from NCUA Chairman Debbie Matz about further discussing or revising the NCUA's role when it comes to this question.

McWatters has no personal opinion about legalization of marijuana at either the state or federal level. But now that issue is out in the open, the board member would like to see more thought given to what legalization means from a social and financial perspective.

“I think people don't think through this subject and, given the history of cannabis in this country, they stop at the philosophical level,” McWatters said. “My suggestion is, let's go a step beyond that level, and that's where Colorado is now.”

Potential upcoming referenda in Ohio could change the way that state views both medical and recreational marijuana usage. Although not scheduled for discussion or introduction before 2016, adding Ohio to the list of legal pot-smoking will likely increase the dialogue and expand credit unions' existing concerns in whether or not to serve these member groups, McWatters said.

“One solution for the industry that does not require any changes by Congress or FinCEN may be for a subset of credit unions and banks or a CUSO that specializes in this area to operate with greater economies of scale and bring more of these businesses into the financial service system,” McWatters said. “But you will absolutely have to comply with the laws; otherwise, it will ruin your whole day.”