People covered by UnitedHealthcare no longer have health insurance access at Northwest Healthcare, which runs Northwest Hospital, the Oro Valley Hospital and a network of affiliated physicians.
The two companies had been negotiating for several months over how much United would reimburse Northwest for the services it provides patients. Those talks continued over the weekend and no agreement was reached.
A statement from Northwest said United rejected all of its proposals and a request for a contract extension.
"We believe United is not acting in the best interest of their members or our community," Northwest said in the statement.
United issued a statement saying Northwest had turned down its offer for a five-year agreement, in which "we made significant compromises ... and agreed to continue paying Northwest Healthcare the same rates over the next three years as we had been previously."
United said Northwest wants a 27 percent increase in payment rates over three years. Northwest said United wants a 25 percent reduction in payment rates.
Patients with United will have to pay out of pocket or get care at a medical center that accepts the insurer. United's statement said patients in ongoing treatment can request a "continuity of care benefit" by calling the telephone number on their health insurance ID cards.
United estimates that around 46,000 of its members in Tucson receive some sort of treatment or care through Northwest Healthcare.