COLUMBIA — A South Carolina legislator has filed a defamation lawsuit over an anonymous letter mailed to her Spartanburg County constituents that suggests she had an affair with Gov. Mark Sanford.

State Rep. Rita Allison of Lyman, along with the state Republican Party, filed the lawsuit Thursday against an unnamed “John Doe.” The 69-year-old grandmother says the letter mailed to voters Aug. 10 crossed the line beyond dirty politics and into a character assassination.

Allison says she filed the lawsuit to make a stand that spreading lies is unacceptable, especially anonymously.

Allison is a six-term lawmaker and former education adviser to Sanford. She said the governor should resign after he revealed his extramarital affair with an Argentine woman in June.