Railroad Retirement garnishment

My father had his checking account garnished by a credit card company for 98% of his monthly Railroad Retirement Pension wages. I've read a bit of information that railroad retirement pensions cannot be garnished by a credit card company. Is this true?

I also read on one of the forums here that credit card companies can garnish your bank account as a way around garnishing the pension directly. The credit union my father banked with only allows employees and retirees related to the railroad and other related firms and union members to bank with them, and in turn would know that my father is a railroad retiree. Since the garnishment has already happened, is there a way to recover those garnished wages taken from the bank?