I just learned that, unlike banks, credit unions need not honor the posted APY on non-CD accounts. This is because at a credit union, posted dividend rates are considered prospective in nature. Until formally declared and paid at the end of the statement period, the rate is subject to change retroactively to the beginning of the statement cycle. In my case, the credit union had posted a 2% APY, but declared a 1.75% dividend at the end of the month. All perfectly legal under NCUA regulation (12 CFR 707.3).