Unless you are going to ask them for something (like a forbearance), you don't need to tell them.
However, I caution you on your desire to continue paying them. If you have no income...you need to drastically reduce your expenses now. I am not saying don't pay your credit cards, but people tend to exhaust their cash very quickly because they don't change their spending habits fast enough when income stops. Many run out of cash and end up filing bankruptcy when it would have been smarter to file bankruptcy as the initial response to income loss.
Anyway, just something to think about. Obviously I don't know your specific circumstances.
There is no requirement to tell them your income changed. It sounds like you use the cards for convenience and, maybe, to build credit - you use them and pay them off right away. As Matt notes, the big thing is to make sure you have a financial plan in place to be able to live off your savings.
Please remember to mark my answer as "helpful" or even the "best" if that is the case. My response is general information not intended as legal advice or to create an attorney-client relationship. Seek advice from a qualified attorney to see how the law fits your specific facts. I am licensed to practice law in Washington and Oregon. www. RRLawGroup.com