Iowa’s Republican governor signed into law on Friday a measure that ends state civil rights protections for transgender people, a move that L.G.B.T.Q. rights advocates said made the state the first to eliminate such broad and specific protections for transgender people.

Gov. Kim Reynolds, who had previously signed laws restricting gender-transition treatments for minors and sports participation by transgender women, said in a video statement that “before I signed this bill, the Civil Rights Code blurred the biological line between the sexes.”

The Republican-backed bill passed both legislative chambers by large margins despite protests at the State Capitol and warnings from Democrats that the measure could lead to discrimination and harassment.

“This bill creates a caste system where one group of people, Iowa trans citizens, do not have the same set of rights that we have,” State Representative Beth Wessel-Kroeschell, a Democrat, said during a debate over the bill on Thursday.

The signing of the Iowa legislation comes as President Trump’s administration moves to limit official recognition of transgender identity nationally. The administration has sought to end funding for hospitals that provide gender-transition treatments to minors, to bar transgender women and girls from competing in women’s sports, to bar openly transgender people from serving in the military, to house transgender women who are inmates in federal prisons with men, and to no longer reflect the gender identities of transgender people on passports.

The Iowa law defines sex based on a person’s anatomy at birth and removes gender identity from a list of protected groups that employers, businesses and landlords may not discriminate against. The bill leaves in place discrimination protections for gay and lesbian people, which were passed 18 years ago as part of the same state law that had extended protections for gender identity.