A Washington arts council reversed a decision on Thursday to make all of its grantees sign new contracts that several arts groups said would leave recipients open to censorship.

The arts groups who were greenlighted for grants from the council, the D.C. Commission on the Arts and Humanities, which is partially backed by the National Endowment for the Arts, received a letter on Monday. There was an amendment to the original grant contracts that they were instructed to sign to receive the money, for which they had already signed paperwork for.

It stipulated that the work of recipients was susceptible to losing funding if it was “lewd, lascivious, vulgar, overtly political, excessively violent, constitutes sexual harassment, or is, in any other way, illegal.” It did not specify how “overtly political” would be defined, or who would be making those judgments. The decision also came as a surprise to commissioners of the council, volunteers throughout Washington who are supposed to represent the public.

“I first heard about this amendment from a grantee who received the notice,” Kay Kendall, the chairwoman for the commissioners, said in an email. “And then a tsunami of emails followed, from grantees and fellow commissioners.”

Another commissioner, Josef Palermo, criticized the agency for not consulting commissioners. It is unclear who made the decision to add the amendment. Inquiries to top officials at the council went unreturned.

“I wish that the commissioners had been consulted on this amendment before it went out,” Mr. Palermo said in an interview. “The fact that we were not is very problematic.”

After the amendment began circulating, arts groups mobilized. The National Coalition Against Censorship circulated a letter that said, “As supporters of an open cultural sphere, we strongly oppose this blatant — and likely unconstitutional — attempt to censor artists and cultural institutions.” Groups like PEN America and Transformer, a Washington-based arts nonprofit and also a grant recipient, co-signed the letter. The Warhol Foundation released a statement that said, “The amendment is a blatant attack on free speech and a direct threat to all artists and nonprofit organizations that produce challenging work.”

As the week progressed, pressure increased on Muriel Bowser, the city’s mayor. Jack Evans, a councilman, called on Ms. Bowser to rescind the amendment. By Thursday evening, grantees received word that, indeed, it was no more. It remains unclear how or why the decision was made.

“The Bowser administration stands firmly behind our shared D.C. values and will always strive to uphold our mission of service to the District and its residents,” the council said in a statement. “The D.C. Commission on Arts and Humanities believes deeply in the right to freedom of expression and would never seek to violate that right by censoring the work of any grantee.”