Bloomberg Law: INSIGHT: State Investigations—50 Takes on Subpoena, Privilege, Document Rules by Brendan Parets:
The law of federal congressional investigations is relatively developed and has accelerated with the inquiries into the Trump administration, spurring numerous cases on contested subpoenas. But on the state level, differences in rules for legislative investigations can abound.
While less visible than Congress, state legislatures may also investigate individuals and organizations. Many concepts in state legislative investigations are similar to congressional investigations and the protections offered witnesses tend to be the same. But differences exist among the 50 states, and organizations and individuals facing state legislative investigations can face unfamiliar rules and processes.