At the University of North Carolina, three incoming freshmen sue over a reading assignment they say offends their Christian beliefs.
In Colorado and Indiana, a national conservative group publicizes student allegations of left-wing bias by professors. Faculty get hate mail and are pictured in mock ''wanted" posters; one college says a teacher received a death threat.
And at Columbia University in New York, a documentary film alleging that teachers intimidate students who support Israel draws the attention of administrators.
The three episodes differ in important ways, but all touch on an issue of growing prominence on college campuses.
Traditionally, clashes over academic freedom have pitted politicians or administrators against instructors who wanted to express their opinions and teach as they saw fit. But increasingly, it is students who are invoking academic freedom, claiming biased professors are violating their right to a classroom free from indoctrination.
In many ways, the trend echoes past campus conflicts -- but turns them around. Once, it was liberal campus activists who cited the importance of ''diversity" in pressing their agendas for curriculum change. Now, conservatives have adopted much of the same language in calling for a greater openness to their viewpoints.
Similarly, academic freedom guidelines have traditionally been cited to protect left-leaning students from punishment for disagreeing with teachers about such issues as American neutrality before World War II and US involvement in Vietnam. Now, the same guidelines are being invoked by conservative students who support the war in Iraq.
To many professors, there is a new and deeply troubling aspect to this latest chapter in the debate over academic freedom: students trying to dictate what they do not want to be taught.
''Even the most contentious or disaffected of students in the '60s or early '70s never really pressed this kind of issue," said Robert O'Neil, former president of the University of Virginia and now director of the Thomas Jefferson Center for the Protection of Free Expression.
Those behind the trend call it an antidote to the overwhelming liberal dominance of university faculties. But many educators, while agreeing that students should never feel bullied, worry that they merely want to avoid exposure to ideas that challenge their core beliefs -- an essential part of education.
Some also fear teachers will shy away from sensitive topics, or fend off criticism by ''balancing" their syllabuses with opposing viewpoints, even if they represent inferior scholarship.
''Faculty retrench. They are less willing to discuss contemporary problems, and I think everyone loses out," said Joe Losco, a professor of political science at Ball State University in Indiana who has supported two colleagues targeted for alleged bias. ''It puts a chill in the air."
Conservatives say a chill is in order.
A recent study by Daniel Klein, a researcher at Santa Clara University in California, estimated that among social science and humanities faculty members nationwide, Democrats outnumber Republicans by at least seven to one; in some fields it is as high as 30 to one. And in the last election, the two employers whose workers contributed the most to Senator John F. Kerry's presidential campaign were the University of California system and Harvard University.
Many teachers insist personal politics do not affect teaching. But in a recent survey of students at 50 top schools by the American Council of Trustees and Alumni, a group that has argued there is too little intellectual diversity on campuses, 49 percent reported that at least some professors frequently commented on politics in class even if it was outside the subject matter.
Thirty-one percent said they felt there were some courses in which they needed to agree with a professor's political or social views to get a good grade.
Leading the movement is the group Students for Academic Freedom, with chapters on 135 campuses and close ties to David Horowitz, a onetime liberal campus activist turned conservative commentator. The group posts student protests on its website about alleged episodes of grading bias and unbalanced, anti-American propaganda by professors -- often in classes, such as literature, in which it is off-topic.
Instructors ''need to make students aware of the spectrum of scholarly opinion," Horowitz said.
''You can't get a good education if you're only getting half the story."
Conservatives say they are discouraged from expressing their views in class, and are even blackballed from graduate school slots and jobs.
''I feel like [faculty] are so disconnected from students that they do these things and they can just get away with them," said Kris Wampler, who recently publicly identified himself as one of the students who sued the University of North Carolina. Now a junior, he objected when all incoming students were assigned to read a book about the Koran before they got to campus.
''A lot of students feel like they're being discriminated against," he said.
His and other efforts are having mixed results. At the University of North Carolina, the students lost their legal case, but the university no longer uses the word ''required" in describing the reading program for incoming students (the plaintiffs' main objection).
In Colorado, conservatives withdrew a legislative proposal for an ''academic bill of rights" backed by Horowitz, but only after state universities agreed to adopt its principles.
At Ball State, the school's provost sided with professor George Wolfe after a student published complaints about Wolfe's peace studies course, but the episode has attracted local attention. Horowitz and backers of the academic bill of rights plan to introduce it in the Indiana Legislature -- as well as in up to 20 other states.
At Columbia, anguished debate followed the screening of a film by an advocacy group called The David Project that alleges some faculty violate students' rights by using the classroom as a platform for anti-Israeli political propaganda (one Israeli student says professor taunted him by asking, ''How many Palestinians did you kill?"). Administrators responded this month by setting up a new committee to investigate students' protests.
In the wider debate, both sides cite the guidelines on academic freedom set out in 1915 by the American Association of University Professors.