SAN FRANCISCO (CBS/AP) — The San Francisco city attorney has filed a lawsuit against the state of Nevada seeking reimbursement for treatment of psychiatric patients allegedly bused to the city.

City Attorney Dennis Herrera filed the suit Tuesday in San Francisco Superior Court.

Herrera had threatened to sue the state after an investigation he says identified 500 discharged patients transported to California since 2008.

He asked for reimbursement and an agreement that Nevada would change its discharge policies by Monday.

Nevada pushed back against Herrera Monday, saying he hasn’t made an adequate case for why the city deserves a half-million dollar reimbursement for treatment of psychiatric patients who were allegedly bused to the city.

In a letter dated Monday, Nevada Chief Deputy Attorney General Linda C. Anderson wrote that documents the state provided to San Francisco City Attorney Dennis Herrera “demonstrate that the policies are appropriate and that proper discharges were made.”

“You made a demand for approximately $500,000 but you fail to provide details to support your claim including how you identified the 20 patients,” said the letter. “Moreover, you do not provide sufficient explanation of your legal theory or standing for the initiation of a lawsuit by you on behalf of the `affected California cities and counties.”‘

Last month, San Francisco threatened to sue Nevada on behalf of local governments in California, saying he’d identified 500 psychiatric patients who were discharged in Nevada and transported to California since 2008.

Of those, 24 ended up in San Francisco and 20 needed emergency treatment upon their arrival, Herrera said.

The city attorney requested $500,000 for San Francisco and told Nevada officials to improve their policies on out-of-state transportation, indicating he’d sue if Nevada didn’t strike an agreement by Monday.

Officials with the Nevada Department of Health and Human Services said they’ve conducted their own review of 1,473 bus tickets purchased in the past five years, which account for about 5 percent of total discharges. In 10 of those cases, state officials said there wasn’t enough documentation to know whether hospital staff had confirmed there was a support structure waiting for the patient at their destination.

Anderson contended both states are impacted by patients moving across state lines, citing a recent report of a woman with mental illness who was sent from California to Nevada. She added that many patients in Nevada’s mental health facilities are California residents.

Nevada officials also pointed to a similar program run by San Francisco, “Homeward Bound,” that provides homeless people a bus ticket back to family and friends.

“We believe that government officials would benefit from better communication and collaboration on protocols to address the needs of these patients rather than trying to allocate financial responsibility through litigation,” Anderson wrote.

(Copyright 2013 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)