Government guidance intended to increase availability of banking services, such as savings accounts, to marijuana shops.
The Obama administration has sought to lessen the fear of prosecution for banks doing business with licensed marijuana companies, further encouraging US states such as Colorado and Washington that are experimenting with legalising the drug.
The Justice and Treasury departments outlined the policy in writing to federal prosecutors and financial institutions nationwide, the Reuters news agency reported.
The guidance stopped short of promising immunity for banks, but made clear that criminal prosecution for money laundering and other crimes was unlikely if they met a series of conditions, officials said.
Currently, processing money from marijuana sales puts federally insured banks at risk of drug racketeering charges, and they therefore refuse to open accounts for marijuana-related businesses, the AP news agency reported.
The guidance was intended to increase the availability of banking services, such as savings and checking accounts, to marijuana shops that typically deal in cash.
Last month, Colorado became the first state to open retail outlets legally permitted to sell marijuana to adults for recreational purposes, in a system similar to what many states have long had in place for alcohol sales.
Washington state is expected to follow Colorado's lead.
The number of states approving marijuana for medical purposes has also been growing. California was the first in 1996.
It has since been followed by about 20 other states and the District of Columbia.
