A phone pranking app called Ownage Pranks is facilitating phone calls to people across the United States (and Canada) that leave threatening voicemails about their “derogatory” anti-Donald Trump posts, Gizmodo reports.

Brett Vanderbrook is one such person who says he received a call last week from a random phone number.

“It was kind of threatening,” Vanderbrook told Gizmodo. “I was dumbfounded at first and then creeped out. Then I was angry and that’s when I decided to share it.”

In the call, a man’s voice tells Vanderbrook, “We’ve been monitoring some of your posts and it does seem that you’ve been making some rather negative comments about President Trump.”

“Is that correct?” the man’s voice asks, pausing to wait for a response.

“Listen," the voice continues. "We’re going to have to ask you to lay off on the negative and derogatory posts about President Trump, okay?"

The message later asks recipients whether they “want to make America great again,” and signs off with an ominous “you’ve been warned.”

“We’ll be keeping an eye on you,” the message says. “Have a nice day.”

Other people have reported receiving the call, sharing their experiences across various social media platforms.

According to Gizmodo, the beginning of the message, which is cut off in the various recordings, identifies the caller as “Russell from the Citizens for Trump Foundation,” a grassroots pro-Trump “movement” that formed during the 2016 presidential election. Since Trump took office, the group has raised money through the limited liability company Patriotic Strategies, and actively backs Roy Moore in Alabama’s high-profile Senate race.

It’s unclear whether Citizens for Trump Foundation is actually behind the calls.

Update -- Dec. 1:

A previous version of this report referred to the phone calls as "robocalls." Ownage Pranks reached out to clarify they're not "robocalls" in the traditional sense, because that "[requires] automation and random dialing of a database of numbers," which their app does not. The article has been update to reflect that point.

The company also told RawStory that they have a terms of service agreement which "clearly states that people should only be calling people that they indeed know themselves," but declined to offer information on how those connections are verified. A representative said the "Citizens for Trump" message did originate from one of 80 different scripts available via the app, but did not provide any information on who crafted those scripts or whether they follow a formal review process.

"This is the first time one of them has gotten a response like this, and we’ve since made adjustments to it," Ownage Pranks said.

"We want people to have fun with these and its really disappointing to hear that some people feel attacked by them," the company continued. "... Most of the calls are so outlandish, it's pretty easy for your friends to be able to tell in the end how crazy it is. The fact that people can actually believe that the NSA or some government entity is tapping their searches and telling them to 'knock it off' is sadly something that people may actually be able to believe in this political climate."