“Initially this was voluntary compliance. They’ve refused so now the next step is issuing a subpeona compelling them to testify. It they refuse, then further action can be taken.”
That is what I meant. If they refuse to comply with a subpoena, lock them up.
Correct, although the “further action” is pretty wimpy. Being requested to testify is voluntary, defying a subpoena is still not a criminal offense, and is carried out through the legal system which provides many opportuities to delay and obfuscate. Congressional testimony is really pretty much a request rather than a demand.