The theater itself was closed for asbestos removal last month.
But the Illinois Environmental Protection Agency raised concerns that some of the cancer-causing material wasn't properly disposed of. That has now led to the closure of most of the building.
An attorney for the theater said tests show there is no longer any asbestos threat, and they hope to reopen by Sept. 18.
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"The Rialto is committed to the safety of its employees, tenants, and guests of the Rialto," the attorney said in a statement.
The theater is frequently used for performances and weddings.