BOISE, Idaho (AP) — An Idaho bill banning transgender women from competing in women’s sports despite warnings that such a law is unconstitutional headed back to the House on Monday after being amended in the Senate.

The Senate voted 24-11 to approve the measure that would apply to all sports teams sponsored by public schools, colleges and universities. A girls’ or women’s team would not be open to transgender students who identify as female.

Backers say the law is needed because transgender female athletes have physical advantages. They say that allowing transgender women to compete can limit athletic, economic and self-growth opportunities provided through sports made possible by Title IX.

The 1972 law bars sex discrimination in education and is credited with opening up athletic competition for girls and women.

“It started to level the playing field,” said Republican Sen. Mary Souza. “But now we are in a new crisis. Girls who have been struggling and training and competing in their sport are suddenly confronted by biological males.”

Opponents said the bill discriminates against transgender girls and women, and will subject athletes to invasive tests, causing them to forgo sports altogether.

The original version of the law easily passed in the House. The Senate amended the bill in an attempt to alleviate concerns about such tests. But opponents were unconvinced, arguing anyone from a parent to an opposing player or someone with a grudge could require a student to take a humiliating test.

“It would damage and hurt her reputation and dignity for life,” said Democratic Sen. Michelle Stennett, noting very young girls would be subject to invasive physical exams. “Beyond the medical inaccuracies, this bill risks harming the physical and emotional health of our children.”

Republican Sen. Jim Rice agreed with Souza that males are generally better athletes than females. He said allowing transgender high school students to compete in girls' sports could limit the competitive experiences of others.

“I think that it is important to protect those opportunities for my granddaughters,” Rice said.

Democratic Sen. Maryanne Jordan said there was no need for the law because there were no instances of transgender girls or women competing in Idaho sports. She also said the Idaho High School Activities Association has a policy in place already, as does the NCAA. Both include a requirement for medically prescribed hormone treatment before participating on a girls' team.