People—lawyers or not—who threaten to initiate criminal proceedings against others can land in hot water.
Lawyers who threaten to take opponents to criminal court in order to gain an advantage are generally subject to discipline for unethical behavior. This scenario sometimes arises in particularly contentious cases: Lawyer A threatens to report Lawyer B or Lawyer B’s client to the authorities for some kind of alleged misconduct unless they cave to A’s demands. Of course, if the threatened party has actually committed a crime, that party probably won’t want to report the threat-maker (thereby potentially drawing the interest of law enforcement investigators).
Further, it may be a crime itself to threaten to initiate criminal proceedings against another. In Washington, for example, trying to obtain goods or services from another by threat of criminal prosecution constitutes second degree extortion. (Wash. Rev. Code §§ 9A.56.110, 9A.56.130, 9A.04.110.) (It’s a defense that the defendant reasonably believed the threatened charges to be true and was acting solely to cause the other party to remedy the situation.)
It’s also illegal for a debt collector to threaten criminal action against someone who is late on a bill. (For more information, see this article on debt-collector threats.)
If you’ve been threatened with criminal charges, consult an experienced attorney immediately.