Yesterday I received a writ of execution in the mail from both the garnishees and the law office they are using. I called the law firm and they said it seems like the will freeze my bank accounts. I work for the federal government and have my check direct deposited in the bank that has issued the writ.

Does this mean I will not be able to get my pay out of the bank?
I live in Pennsylvania.

Also, what's the chance that they can garnish my wages?

If the writ has been served on your bank, then yes it means your funds are frozen until releases to the judgement holder. It also means they can garnish your salary.

Were you not aware of the judgment?

Once the money goes into a bank account that is froze or garnished, you will not get any funds out.

You need to stop any direct deposit into that acount ASAP