LOS ANGELES — Cable channel HBO urged critics of its planned slavery-themed drama “Confederate” to reserve judgment until the show develops further, in response to an intense social media campaign demanding that the project be axed.

The hashtag #NoConfederate was a top-trending Twitter topic worldwide on Sunday after April Reign, the woman behind the #OscarsSoWhite campaign two years ago, urged people to send a message to HBO objecting to the show.

Critics of the concept have deemed it both offensive and inappropriate, especially coming from two white male creators, David Benioff and D.B. Weiss, the creators of HBO’s medieval fantasy series “Game of Thrones.”

“We believe the time to speak up is now, before the show has been written or cast. Before @hbo invests too much money into #Confederate,” Reign tweeted, as #NoConfederate became a trending topic during Sunday night’s episode of “Game of Thrones.”

HBO announced last week that “Confederate,” in the early stages of development, would be set in an imaginary world where slavery still exists in the United States and the nation is on the brink of a third civil war.

HBO said on Sunday that while it had “great respect for the dialog and concern being expressed around ‘Confederate,’ it had faith in creators Benioff, Weiss and their black writing partners, Nichelle and Malcolm Spellman.

“The project is currently in its infancy so we hope that people will reserve judgment until there is something to see,” HBO said in a statement.

Responding to the backlash, the “Confederate” creators said last week that neither they nor the show endorse slavery.

Malcolm Spellman acknowledged that the premise was “weapons-grade material,” but said the series would provide an opportunity to examine how racism and white supremacy are “alive and real” in the United States, more than 150 years after slavery was abolished.

Reign’s Twitter campaign, however, suggested the controversy is unlikely to go away any time soon.

“We did it!!! We trended #1 nationwide & #2 worldwide for most of the hour. THIS is the power of social media, @HBO, & we say #NoConfederate,” Reign tweeted late on Sunday.

The #OscarSoWhite campaign erupted over the dearth of black and brown actors in the 2015 and 2016 Oscar nominations. It prompted a boycott of the annual ceremony by some filmmakers, and forced the Academy of Motion Picture Arts and Sciences to broaden its membership to include more women, people of color, and younger people.