Two unnamed students who were enrolled in Valencia College’s Medical Diagnostic Sonography program in 2013 are suing the Florida school, claiming they were forced to undergo invasive and sometimes painful transvaginal ultrasounds nearly every week.

The school says it is “accepted practice” to use students as models in sonography training programs. Participating in the ultrasounds is voluntary, the school said.

But the two female students who filed a lawsuit in federal court last week say their academic standing and career prospects were threatened if they didn’t agree to participate. The practice was “widespread” and “so permanent” that it more or less constituted a “custom” at the school, according to the lawsuit.

A transvaginal ultrasound is a procedure that involves inserting a probe into a woman’s vagina to check for pregnancy, fertility or other reproductive problems. The probe is covered with a condom, then lubricated and inserted into the vagina. According to the lawsuit, the probe can be uncomfortable or painful and isn’t recommended for female patients who have not had sexual intercourse.

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During orientation for the program, the lawsuit said, a second-year student explained the faculty believed that “students should undergo invasive transvaginal ultrasound procedures in order to become better sonography technicians.” The second-year student was nicknamed the “TransVag Queen,” according to the lawsuit.

In the fall of 2013, the two students who would later file suit expressed concerns about the practice to Barbara Ball, chair of Valencia State’s medical diagnostics sonography program, according to the lawsuit.

“One of the many concerns being the program had a male student who would also probe the female Plaintiffs on a regular basis,” the suit claims.

According to the suit, Ball told the students that they could “find another school if they did not wish to be probed.”

The suit claims that administrators threatened to lower the plaintiffs’ grades and interfere with their future employment prospects by “blacklisting” them at Central Florida hospitals if they didn’t submit to the probes.

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“Although it was stated in orientation it was voluntary, it became increasingly clear it was not,” said the women’s attorney, Chris Dillingham, according to CNN. “This is a very expensive program, these are young women. … I’m not a doctor but they have suffered significant psychological damage

At one point, during an ultrasound session, the suit claims, Ball, the program chair, commented that a female student was “sexy” and should be an “‘escort girl’ (prostitute).”

Female students would get undressed in the bathroom, cover themselves with towels and walk across the classroom to reach one of the sonography stations, with teachers and classmates watching, according to the lawsuit.

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“In some cases, the student would have to sexually ‘stimulate’ Plaintiffs in order to facilitate inserting the probe into Plaintiffs’ vaginas,” the suit claims. “Plaintiffs experienced discomfort and embarrassment each time they had to endure this forced probing of their sexual organs.”

In a statement to the Orlando Sentinel, Valencia State College defended the use of student models as part of the training:

The use of volunteers—including fellow students—for medical sonography training is a nationally accepted practice,” the school said in a statement according to the Orlando Sentinel. Valencia’s sonography program has upheld the highest standards with respect to ultrasound scanning for educational purposes, including voluntary participation and professional supervision by faculty in a controlled laboratory setting. Nonetheless, we continue to review this practice and others to ensure that they are effective and appropriate for the learning environment.”

Valencia State ended the practice after the students’ lawyers contacted the school, according to the lawsuit.

Both students eventually resigned from the school’s sonography program.