Bayfront Health System will no longer accept Aetna insurance in most cases.
The two sides could not agree to higher rates during recent contract negotiations, though they did not rule out a future contract.
Aetna, which insures 300,000 members across Tampa Bay, pays the hospital at least 30 percent less than other health insurers, said Bayfront chief financial officer Bob Thornton.
"We were really asking Aetna to bring us up to fair market rates, and we weren't able to get there with them over several weeks of negotiation," he said.
The contract officially expired Friday.
Bayfront, which includes Bayfront Medical Center, will continue to accept Aetna for trauma patients and those with out-of-network benefits.
"Anybody in the community that needs emergency medical care can come to Bayfront," Thornton said. "We are not turning anybody away."
Thornton said Bayfront and Aetna are also working with patients who need ongoing care and have pre-scheduled treatments to make sure they are not affected by the change.
Many other area hospitals still accept Aetna, including St. Petersburg General Hospital, Tampa General Hospital, St. Anthony's Hospital and Morton Plant Hospital.
Aetna spokesman Walter Cherniak said the health insurer has had a contract with Bayfront for at least 12 years.
Health care costs are constantly on the rise, he said, and Aetna could not increase payments as Bayfront had requested without raising customer rates. Cherniak said Aetna did propose a multiyear contract in which the payments would increase each year but was still unable to reach an agreement with Bayfront.
"We would certainly like them to be in our network, but we also have an obligation to our customers to keep a hand on rising health care costs as best we can," Cherniak said. "We were not able to reach common ground."