Federal loans don't have a statute of limitations, so they can use any of their available tools to collect at any time. I know that tax returns are often off-set without warning to the borrower, and garnishments as well, I haven't heard of many bank accounts being frozen without warning, but that doesn't mean it doesn't happen.
Contact the collection agency and make a plan to get your loans out of default - if you don't want to do rehab, just consolidate since the loans no longer appear on your credit. That will get them back in good standing immediately, and if you choose an income-driven payment plan your payments could be as low as $0.
