All banks have the ability to deny service at any time, although few exercise it. No payments are made to a bank to keep or operate an account (withdrawal and low balance fees do not apply), therefore it is a complimentary service. One can ask the bank why the accounts are being closed, but it is often because they have been informed by their lawyers that they are no longer able to fractionalize on the account's deposits (turning $1 into $10 for their private benefit). This happens most often with small/local banks, and virtually never with large multi-national banks such as Chase Manhattan, Bank of America, HSBC and others of the same ilk.
One can ask what can be done to salvage the relationship; however, it's going to often be dependent on the removal of all deposits/withdrawals in lawful money. It is better to move onto a larger bank that does not care about accounts dealing in lawful money, as they rely on 99% of their account holders being unaware of fractionalization and lawful money redemption.
So the question is, what is more important - reducing one's income liability OR retaining the relationship with the bank?