Updated

San Francisco is threatening to sue Nevada for allegedly dumping some 500 psychiatric patients in California.

The San Francisco Chronicle says City Attorney Dennis Herrera plans to send a letter Tuesday to Nevada Attorney General Catherine Masto.

The paper says a draft of the letter threatens a class-action lawsuit against Nevada unless it reimburses California cities and counties for the costs of dealing with the patients and adopts interstate transfer rules for patients.

The letter says the patients were discharged from a state-run psychiatric hospital in Las Vegas since April of 2008 and got one-way bus tickets to California. Two dozen sent to San Francisco were broke, homeless and mentally ill.

The Chronicle says officials at Masto's office and Nevada's health department declined to comment.