How dare she!

More than 3,500 students, teachers and parents have signed an online petition in just two days this week demanding the ouster of the principal of famed La Guardia High School of Music & Art and Performing Arts because she — gasp! — has the audacity to stress academics in addition to performing talent.

“Since the 2013 arrival of Principal Dr. Lisa Mars, LaGuardia’s admission process has been radically altered in favor of academic scores and attendance records,” the change.org petition charges.

“With these new admission criteria, talent counts for only 14% of the admission decision. As a result, hundreds of qualified and gifted students have been denied admission.”

Student talent had previously counted for well over 50 percent in the admissions process at the Upper West Side school, sources said.

The school, which was the inspiration for the 1980 movie “Fame’’ as well as a TV series, boasts star graduates ranging from Nikki Minaj to Al Pacino.

It is the only specialized city high school that doesn’t base admissions solely on a single test, instead allowing its administrators to vet prospective students on a range of abilities.

The principal’s critics gripe that the new system is better suited for future Einsteins rather than De Niros — and was changed without proper input from the school community.

Yet “despite this illegal change in the admissions process and overwhelmingly negative ratings from La Guardia teachers and staff, Dr. Mars is being considered for tenure,” the petition reads.

Mars was installed as principal by Schools Chancellor Carmen Fariña in 2013.

A DOE spokesman said Mars is following all regulations and noted that only applicants who audition successfully are then vetted academically.

Critics claim that festering dissatisfaction with the school’s acceptance policy has caused unusually high staff turnover.

“This year alone nearly 18% have left,” the petition reads. “Dr. Mars, who has had little experience in educating artistically talented students, has hired questionable replacements.”

As word of the online campaign grew this week, alumni have chimed in to voice their concerns for La Guardia’s future.

“Allow the artistic kids to thrive through their creativeness,” wrote alumni José Torres of The Bronx on the site. “It might be the only thing they have.”

The high school moved to its current location near Lincoln Center from Midtown in 1984.