The Biden administration on Tuesday ordered Arizona Gov. Doug Ducey to stop using the state’s federal pandemic funding on a pair of new education grants that can only be directed to schools without mask mandates.

In a letter to Ducey, the Treasury Department said the grant programs are “not a permissible use” of the federal funding. It’s the latest attempt by the Biden administration to push back against Republican governors who have opposed mask mandates and otherwise sought to use federal pandemic funding to advance their own agendas.

Ducey launched a $163 million grant program using federal funding he controls, but he made it available only to schools without mask mandates. He also established a $10 million program that offers vouchers to families at public schools that require masks or that tell students to isolate or quarantine due to COVID-19 exposure.

In the letter, Deputy Treasury Secretary Wally Adeyemo said the conditions “undermine evidence-based efforts to stop the spread of COVID-19.” He asked the state to explain how it will “remediate” the problem within 30 days.

The Education Department in August opened civil rights investigations into five Republican-lead states that forbid mask mandates in schools, saying such actions may violate the rights of students with disabilities.