Generally, unemployment benefits are protected from garnishment and beings used to satisfy most payment orders under MGL c. 151A, sec. 36. However, government backed loans may have exceptions from this.
If the payments are voluntary, you may be able to stop. In Massachusetts, a creditor needs to seek court permission to garnish ones wages. Under Federal law there is an administrative garnishment procedure relative to student loans, but these provide an opportunity for a hearing and appear to only be able to garnish wages.
It may be best for you to speak to the unemployment office about what garnishments can be made on your unemployment benefits; and an attorney will be able to offer you advice on the topic as well. If the collectors threatened to garnish your unemployment then you should speak to an attorney about any possible FDCPA, or other collection law violations.
This answer is provided in response to a "hypothetical" question and provided for general, informational purposes and does not create an attorney/client relationship. The information presented is not legal advice and may change based additional information and research. It is recommended that you speak to an attorney to discuss your specific legal issues.