The air traffic control tower was closed for cleaning after 3 workers tested positive for COVID-19.
RELATED: Midway Control Tower workers test positive for coronavirus; hundreds of flights canceled at airport
Other airlines are flying into and out of Midway, but the majority of flights are on Southwest.
There are more than 150 Southwest flight cancellations.
The airline has offered flexible accommodations to all impacted customers.
It is not known when the airline will resume operations.