The executive director of the Center for Immigration Studies (CIS) is claiming that Twitter blocked the group from promoting a tweet that included the words "illegal aliens."

"Twitter just rejected paid promotion of the tweet below, saying: "This determination is based on the following Twitter Ads policy: Hateful Content," executive director Mark Krikorian tweeted Tuesday.

He added, "It's because it contains the phrase "illegal alien", which @TwitterAdsHelp deems unacceptable."

The tweet in question featured a video from The Daily Caller. The video of "illegal aliens pouring across the border," CIS argued, "reminds us why we need a wall."

Krikorian claimed Twitter didn't let the group pay to promote the tweet, and said another tweet — which included the words "criminal aliens" — was also denied.

CIS argued that while Twitter allegedly deemed the posts "Hateful Content," the term "'illegal aliens' has been used in both federal law and by the Supreme Court."

A Twitter official told Fox News the decision to block the promoted tweet was an error and overturned.

The controversy follows accusations that Twitter censors conservatives on its platform.

Twitter CEO Jack Dorsey told the House Committee on Energy and Commerce last week that the company "does not use political ideology to make any decisions, whether related to ranking content on our service or how we enforce our rules. We believe strongly in being impartial, and we strive to enforce our rules impartially,” he said.