Didn't File Taxes — further steps and repercussions?

If I didn’t file or pay taxes two years ago, what are the possible repercussions? My main concern is persecution/legal action.

Does the IT department first have to send a notice to file and pay (with the accrued interest + fine etc) and can only persecute if there is no action or response from recipient? Or can they directly take legal action against me without any notice? Is there anything I can do now to remedy this situation?