Ashton P. Woods, a community activist who is running for Houston City Council, denounced the policy as elitist and a form of respectability politics. “Most of the parents likely cannot afford to comply with this dress code,” he tweeted.

The principal, Ms. Outley Brown, who is black, did not respond to a request for comment on Wednesday.

The Houston Independent School District, the largest school district in Texas, declined to comment.

Dorinda Carter Andrews, the associate dean for equity and inclusion for the college of education at Michigan State University, said that educators have the right to be clear about what kind of attire is appropriate in schools, including which clothing is too revealing. But she said the policy in question inappropriately included rules against hair coverings and housewear.

“There is a fine line here around a socially constructed high standard that is based on norms that aren’t inclusive,” she said, adding that black women’s bodies and hair in particular have been policed historically.

“That has been so problematic historically and in contemporary times for black women, because our hair is like a representation of self,” she said.

The idea of imposing restrictions on parents’ dress has taken root in fits and starts in recent years, primarily in an effort to discourage adults from wearing inappropriate or revealing clothing on school campuses. A bill in Tennessee that would have required school districts to establish codes of conduct for everyone on school property stalled this year. In 2014, a school board in Florida considered, but ultimately rejected, imposing a dress code for parents.

The policy in Houston is not without its supporters. Online, some people spoke up in agreement, lamenting that a policy asking parents to dress appropriately had to be written out in the first place.