State tortious interference claim requires the specific intent to interfere with the business relationship.
Even for a requirement or output contract, state statute of frauds requires a writing enforceable against the deft for any claim arising from the transaction.
http://www.opn.ca6.uscourts.gov/opinions.pdf/18a0162p-06.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.