I have to research it to be able to speak knowledgeably but have they said why they don't have to honor the lease? If they say the law allows them to terminate the lease given the change of usage of the premises, ask them to provide the statute that allows them to terminate existing leases.
Offhand I don't know if they can or cannot. Some states do allow similar issues to allow the termination of existing leases so it may not be so far fetched but, if they are going to claim they do not have to honor the lease, they should be able to cite law to back them up.

