Supporters of the legislation contended marijuana businesses have trouble finding credit unions and banks to provide services to them even in states where marijuana is legal. The problem, they said, is that it remains illegal on the federal level.

"I have significant concerns that the SAFE Banking Act does not address the high level potency of marijuana, marketing tactics to children, lack of research on marijuana's effects, and the need to prevent bad actors and cartels from using the banks to disguise ill-gotten cash to launder money into the financial system," Crapo said as he released his list of concerns.

Crapo listed several options for amending the bill to make it more acceptable, including:

• Adding a public health warning on products in states where cannabis is legal.
• Shoring up federal investigative programs to help ensure that "bad actors" do not use the financial system to launder money.
• Accepting states' right in interstate banking for institutions that do business in multiple states.
• Adding provisions to the bill to prohibit "Operation Choke Point"-type programs. Operation Choke Point was an Obama Administration program intended to hold financial institutions accountable for processing transactions they knew were fraudulent. Critics said the program allowed financial institutions to decide not to provide services to controversial businesses, such as gun dealers.

Crapo has asked specific questions about each of those options and asked interested parties to send his staff suggestions about what should be added to the measure.

Crapo's comments and request are likely to delay Senate consideration of marijuana banking legislation.

Financial services organizations said they plan to work with Crapo to try to make him more comfortable with the issue.

"America's credit unions are eager to continue engaging with the Chairman as he seeks a solution that enhances community safety through access to mainstream financial services," CUNA Chief Advocacy Officer Ryan Donovan said.

"ABA, like many other stakeholders, has already provided the committee relevant information on several of the issues identified by the chairman including legacy cash, interstate commerce and 'Operation Chokepoint,'" James Ballentine, the ABA's EVP of congressional relations, said. "We continue to believe that the SAFE Banking Act responsibly addresses the current legal limbo over cannabis banking, and a strong bipartisan majority in the House shares that view."