Michael Lohan is threatening ex-wife Dina Lohan -- either stop accusing him of rape, or face his legal wrath.
Michael's attorney just sent a cease-and-desist letter to Dina -- following a recent interview in which Dina claimed Michael raped her during a coke binge in 1990.
In the letter, Michael's attorney calls Dina's allegations "false, defamatory, and unlawful."
In the letter the lawyer claims Dina has been harassing Michael of late by leaving a slew of messages on his phone and on the Internet.
Michael wants Dina to shut her mouth and stop contacting him once and for all -- or he'll sue.