Credit unions aren't strangers to crowdfunding. At least one, the Buffalo, N.Y.-based Good Neighbors Federal Credit Union, is using it to raise enough capital to launch; others have teamed up with crowdfunding platforms to support causes such as buying school supplies. Now they may also be able to help investors and businesses find each other.

Through a link embedded on a participating credit union's website, members will see a list of businesses looking for capital, Jeffreys explained. The list is sortable by location, funding level, industry sector and other factors. If members are interested in investing in a company, they can arrange to transfer money right out of their accounts and into an escrow account, he said.

Businesses have to meet their capital-raising goals in order for deals to close. If an entrepreneur wants to raise, say, $25,000 in 30 days and only $15,000 comes in, for example, everyone gets their money back and the deal ends, Jeffreys explained. The credit union doesn't hold stakes in the capital-seeking companies; it simply introduces the parties.

Credit unions pay a one-time setup fee of about $10,000, he said. For the deals they introduce to the platform that fund, the credit union gets about 10% of the 2% to 5% origination fee.

Crowdfunding probably won't generate much revenue for credit unions, but it could create valuable reputational capital because many members will probably invest locally, he said.

"I think it's really more of a strategy," he said. "How does the credit union position itself more to be that local provider, to be that pillar? How do we help small businesses and consumers interact? How do we create these virtuous cycles?"

He added, "My guess is this is not going to be one of those programs where in four or five years there's going to be a thousand credit unions on it. I would think it's more, who are the progressive credit unions that really want to be tied in to their community?"

Still, Jeffreys expects about two dozen credit unions to be signed up by this time next year. He said he isn't sure how much capital might flow through them.

Judging by one industry report, though, it could be a lot. Crowdfunding is growing rapidly around the world, raising $16.2 billion in 2014. That's a whopping 167% increase over 2013, when $6.1 billion was raised, according to Crowdsourcing.org, which expects the dollars raised to double in 2015 to $34.4 billion. North America leads the world in crowdfunding volume, growing by 145% from 2013 to 2014 and raising $9.46 billion. There are at least 1,250 active crowdfunding platforms in the world, it said.

Callahan said it expects crowdfunding to go live in mid-May – 180 days after the SEC posts the rule in the Federal Register.