Election judges in Chicago received mysterious automated phone calls with false instructions over the weekend, the Chicago Sun Times reported.

Election officials said the calls were part of “a serious attempt to disrupt” the voting process.

Some of the calls informed election judges, who are in charge of running polling places, that they needed to undergo additional training. Other calls told them that they were required to vote a certain way in order to work as election judges.

Jim Allen, a spokesman for the Chicago Board of Elections, said they’re unsure how many of the misleading calls went out.

“Given the level of response that we received, we suspect it was a large number of people — we don’t know how large,” he told the Sun Times.

Election judge Danny Bravman said he received two phone calls telling him he needed to attend training at “very out-of-the-way locations.”

“If I call back the number, it says that the message originated from a marketing firm or a paid political organization,” Bravman said. “I haven’t received any official correspondence about additional training sessions. So it seems rather obvious that someone is impersonating the board of elections.”

The Cook County Republican Party told the Sun Times that they were not behind the calls, and the Democratic Party did not return the Sun Times’ phone call.