The California Rosenthal Act, or Rosenthal Fair Debt Collection Practices Act, or RFDCPA - if you like initials, is very similar to the FDCPA. There are some differences. One of the big differences is that the Rosenthal Act requires a debt collector to include a special notice.
California Civil Code 1812.700 states that the notice must read "The state Rosenthal Fair Debt Collection Practices Act and the federal Fair Debt Collection Practices Act require that, except under unusual circumstances, collectors may not contact you before 8 a.m. or after 9 p.m. They may not harass you by using threats of violence or arrest or by using obscene language. Collectors may not use false or misleading statements or call you at work if they know or have reason to know that you may not receive personal calls at work. For the most part, collectors may not tell another person, other than your attorney or spouse, about your debt. Collectors may contact another person to confirm your location or enforce a judgment. For more information about debt collection activities, you may contact the Federal Trade Commission at 1-877-FTC-HELP or www.ftc.gov."
This is a separate notice under the Rosenthal Act then the notice under the FDCPA. So, if you get a letter from a debt collector and you live in California, they must comply with BOTH notice requirements. If the letter does not have both (and check the back of the letter to see if it is printed there), then talk to an attorrney to see if you have a cause of action (right to sue) against the debt collector.