Another common requirement for high-interest checking depositors is to sign up for direct deposit on their accounts, Kelly says.

Direct deposit is important for credit unions because when money is moved into an account on a regular, automatic basis, that account is more likely to be the member's primary transactional account, he says.

With transactional accounts, credit unions have more opportunity to make revenue through fees paid by debit card merchants, for example, says Kelly. "The better the chance that the credit union earns revenue and profit, the more likelihood that the credit union can offer a higher interest checking to its members," he says.

As an alternative to direct deposit, some credit unions use automatic withdrawals to let members meet eligibility requirements, Kelly says. This could be useful for entrepreneurs, retired people and others who don't work for companies that offer a direct deposit option but still want high-interest checking, Kelly says.