The Republican senator wrote in another tweet Monday that he met last week with leaders of pilot unions who “expressed deep concern over the vaccine mandates.” A spokeswoman for Southwest pilots said no one at the union had talked to Cruz. A spokesperson for Cruz did not respond to emailed questions from The Associated Press about whether the Republican senator had any firsthand knowledge of pilots or air traffic controllers skipping work.

Republican U.S. Rep. Andy Biggs of Arizona and U.S. Sen. Ron Johnson of Wisconsin also posted the rumors on social media, without offering proof.

Vague, familiar-looking “friend of a friend” stories are a dangerous form of misinformation because they “feel like insider information being shared by individuals directly involved in the action,” according to Rachel Moran, a misinformation scholar at the University of Washington.

Similar unsupported claims circulated online in August, when social media users falsely claimed that flight delays and cancellations out of Fort Lauderdale-Hollywood International Airport were the result of vaccine mandates. In September, false internet rumors swirled that 40% of employees at defense contractor General Dynamics had declined the vaccine and threatened to quit.