Former Rep. James Rogan, a Republican who served two terms, sent an e-mail Wednesday to Andrew Jones, head of the Bruin Alumni Association, saying he didn't want his name connected to the group.
"I am uncomfortable to say the least with this tactic," Rogan wrote in his e-mail. "It places students in jeopardy of violating myriad regulations and laws."
Rogan's resignation follows those of Harvard historian Stephan Thernstrom and UCLA professor emeritus Jascha Kessler, who both quit the board once they learned of the group's activities.
The group has been offering students up to $100 to supply tapes and notes from classes to expose professors suspected of pushing liberal political views on their students.
Jones, 24, a 2003 graduate and former head of the campus Republican group, said he was concerned about the level of professionalism among teachers at the university.
"We're just trying to get people back on a professional level of things," Jones told The Los Angeles Times.
Targeted professors have likened the effort to a witch-hunt.
"Any sober, concerned citizen would look at this and see right through it as a reactionary form of McCarthyism," said education professor Peter McLaren, whom the association named as No. 1 on its "The Dirty Thirty: Ranking the Worst of the Worst."
Advisory board member Shawn Steel, a lawyer who recently served as chairman of the California Republican Party, defended the association.
"Most parents assume students get a square education at a public university, when in fact, there is no real intellectual diversity," Steel said. "If a student says anything positive about Bush, he'll get bashed."