Some banks and credit unions are starting to do business with legal marijuana sellers, The Washington Post reports.

Because marijuana is still illegal under federal law, banks have been reluctant to conduct business with marijuana-related companies. Banks have feared being accused of helping these businesses launder their money. A conviction on charges of federal money laundering can result in decades in prison.

Last month, the U.S. House rejected a measure that would have blocked the Treasury Department from implementing guidelines to make it easier for legal marijuana businesses to conduct banking. Earlier this year, the Obama Administration provided banks with federal guidelines for conducting banking transactions with legal marijuana sellers, enabling a legalized marijuana industry to operate in states that approve it.

Legal marijuana sellers that are barred from utilizing banks cannot safely deposit cash, leaving them vulnerable to criminals and robbery. Also, state governments that allow marijuana sales want a channel to properly receive taxes from legal marijuana businesses.

A Treasury Department official said this week that 105 banks and credit unions are doing business with legal marijuana sellers. This suggests the federal guidelines are starting to work, the newspaper noted. “From our perspective, the guidance is having the intended effect,” said Jennifer Shasky Calvery, Director of the Treasury Department’s Financial Crimes Enforcement Network. “It is facilitating access to financial services, while ensuring that this activity is transparent and the funds are going into regulated financial institutions.”

Banks are still apprehensive about raising concerns of regulators by conducting business with marijuana sellers, according to Don Childears, President of the Colorado Bankers Association. He called on Congress to intervene.

Taylor West, a spokeswoman for the National Cannabis Industry Association, said, “Our members that are working with the banks are being told not to talk about it.” She said the federal guidelines are “so heavy on regulation . . . it has not led to a tidal wave of openings in a way that we had hoped.”