Here's the deal ... on Monday, Gov. Brad Little signed off on House Bill 500 -- also known as the "Fairness In Women's Sports Act."

The Bill says "athletic teams or sports designated for females, women, or girls shall not be open to students of the male sex." It's aimed at sports leagues connected to the public school system.

In other words, people born with male reproductive organs -- who transition to female -- will not be allowed to compete in "women's" sports.

The issue has made tons of headlines over the past few years -- after transgender athletes began competing (and dominating) in events like weightlifting and track and field.

Some experts believe transgender women have a biological advantage because they were born male genes and bone structure.

But the ACLU believes the new bill is wrong and unconstitutional.

"The ACLU of Idaho condemns Governor Brad Little's decision to sign discriminatory, unconstitutional, and deeply hurtful anti-transgender bills into law."

"Leaders from the business, faith, medical, education and athletics communities will not forget this decision or what it says about the governor's priorities during a global pandemic. The ACLU will see the governor in court."

Boise State runner Lindsay Hecox -- a transgender woman -- spoke out against the bill on Monday saying, "it specifically targets people like me and all transgender female athletes and denies us the opportunity to compete in sports."