Hundreds of Long Islanders may have to find new doctors beginning Thursday after Mount Sinai says it has not reached an agreement with insurance carrier Anthem.

"Despite our good-faith efforts to reach an agreement, Anthem Blue Cross Blue Shield has informed us that we will not be able to come to new terms for commercial, Medicaid, Child Health Plus, and Essential Plans before our current contracts expire on Wednesday, Dec. 31," Mount Sinai said in a statement.

This means 9,000 physicians will be out of network for patients effective Jan. 1.

In March, all of Mount Sinai’s hospitals and facilities will be out of network for those with Anthem insurance.

Anthem representatives could not be immediately reached for comment Wednesday.

The change will not affect people who are in active treatment for serious conditions, such as cancer or pregnancy. Mount Sinai says it must continue in-network access for those patients for a period of time after the Anthem contract expires.