The Texas Tech University system, one of the largest in the state, took steps to restrict academic discussions of gender, directing faculty in a letter circulated on Friday that they “must comply” with an executive order from President Trump recognizing only male and female genders.

The move, apparently a first among large institutions of higher education, raised alarm among professors and advocates of academic freedom across Texas. It signaled that an effort to restrict teaching about transgender people and other gender topics in K-12 classrooms — explicitly prohibited by Texas law — was expanding to colleges and universities, where no such ban exists.

Several other public universities and community colleges have been exploring similar changes regarding the teaching of gender, according the Texas conference of the American Association of University Professors. But outside of Texas Tech, none appeared to have put their guidance into writing yet.

Earlier this year, the Mississippi Legislature passed a law banning diversity, equity and inclusion, as well as “promoting transgender ideology,” in the state’s schools and universities, but a federal judge put it on hold.

On Friday, 16 states led by Democrats, along with the District of Columbia, filed a lawsuit in Oregon to block the Trump administration from requiring them to remove all references to “gender ideology” from sexual education in order to receive federal grant funding.

In a letter to all five of the Texas Tech system’s universities, dated Thursday but circulated widely on Friday, Chancellor Tedd L. Mitchell said that the direction had been part of an effort to remain in legal compliance. It followed weeks of behind-the-scenes discussions among administrators and some faculty.