Parents who were outraged at the NCAA for allowing University of Pennsylvania transgender swimmer Lia Thomas to compete and dominate in women’s competitions wrote a letter to the college athletics’ governing body demanding a rule change.

Thomas, a transgender student at the Ivy League university, dominated the 500-yard freestyle preliminaries and finals at the Zippy Invitational at the University of Akron this month. Thomas earned a winning time of 4:34.06 in the finals, breaking the Ivy League record, and set new school records in the 1,650-yard freestyle and 200-yard freestyle competitions. Thomas previously competed as a man for three years on the school's men's team. Thomas' success on the women’s team has renewed criticism over allowing transgender women to compete against biological females.

CLICK HERE FOR MORE SPORTS COVERAGE ON FOXNEWS.COM

Photo Penn swimmer Lia Thomas

Lia Thomas' participation on women's swim team prompted a letter from parents of teammates. (Penn Athletics)

According to The Daily Mail, parents of about 10 swimmers sent a letter to the NCAA, the Ivy League and Penn athletics officials over their concerns about the integrity of women’s sports.

"At stake here is the integrity of women's sports. The precedent being set – one in which women do not have a protected and equitable space to compete – is a direct threat to female athletes in every sport. What are the boundaries? How is this in line with the NCAA's commitment to providing a fair environment for student-athletes?" the letter obtained by the outlet read.

"It is the responsibility of the NCAA to address the matter with an official statement. As the governing body, it is unfair and irresponsible to leave the onus on Lia, Lia's teammates, Lia's coaches, UPenn athletics and the Ivy League. And it is unfair and irresponsible to Lia to allow the media to dictate the narrative without the participation of the NCAA."

The letter was sent Dec. 5. The NCAA didn’t respond to it.

PENN SWIMMER LATEST EXAMPLE OF TRANS ATHLETE DOMINATING FEMALE SPORTS

The University of Pennsylvania did respond.

"Please know that we fully support all our swimming student-athletes and want to help our community navigate Lia's success in the pool this winter," the school said. "Penn Athletics is committed to being a welcoming and inclusive environment for all our student-athletes, coaches and staff and we hold true to that commitment today and in the future.

"We've encouraged our student-athletes to utilize the robust resources available to them at Penn, and I'd like to share them with you as well."

NCAA president Mark Emmert

NCAA president Mark Emmert didn't immediately respond to the letter. (AP Photo/Matt York, File)

NCAA rules state that a trans woman can't compete with women until after undergoing testosterone suppression treatment for a year. Thomas recently brushed off her critics in an interview, saying the NCAA rules are fair and "promote competition integrity."

The NCAA has defended its policy, which requires testosterone suppression treatment, as part of its vision for "fair competition."

"The NCAA Board of Governors firmly and unequivocally supports the opportunity for transgender student-athletes to compete in college sports," the NCAA said in April. "This commitment is grounded in our values of inclusion and fair competition."

The NCAA has defended its policies regarding trans athletes

The NCAA has defended its policies regarding trans athletes. (AP Photo/Michael Conroy, File)

CLICK HERE TO GET THE FOX NEWS APP

"The NCAA has a long-standing policy that provides a more inclusive path for transgender participation in college sports. Our approach – which requires testosterone suppression treatment for transgender women to compete in women’s sports – embraces the evolving science on this issue and is anchored in participation policies of both the International Olympic Committee and the U.S. Olympic and Paralympic Committee. Inclusion and fairness can coexist for all student-athletes, including transgender athletes, at all levels of sport."

Fox News’ Jessica Chasmar contributed to this report.