The forbidding notices you receive will warn that you have 30 days to respond or suffer the financial consequences. In that 30 days, you may call the IRS to explain that you already have an installment agreement in place, that you are an ‘innocent spouse,’ or other. You may also request a CDP hearing.
If you request the CDP hearing in a timely manner, all punitive actions against you must cease until that hearing is complete. They cannot lien, levy, or garnish until they give you a fair hearing. If you file after that 30 day period, they can move forward with any draconian actions at their disposal. If your collection due process hearing results in a negative outcome and is not appealed, it becomes your ticket to tax court.