Sen. Ted Cruz, R-Texas, took to Twitter late Sunday to speculate about Southwest Airlines’ decision to cancel more than 1,000 flights just days after its pilots’ union asked a court to block the company's new COVID-19 vaccination mandate.

The airline has blamed the cancellations on "disruptive weather" and air traffic control issues. Some Twitter users were suspicious of the timing of the disruption, including the Texas Republican.

"Joe Biden’s illegal vaccine mandate a work!" Cruz tweeted. "Suddenly, we’re short on pilots & air traffic controllers."

The airline announced last week that—due to the new rules from the Biden administration—its workers must be vaccinated against COVID-19 and have until Dec. 8 to be fully vaccinated. Workers are allowed to seek medical or religious exemptions.