Over the phone? While in another's office during a meeting? While in another's house? Is there a statute or particular caselaw that governs?
Construction / Development Lawyer
California Penal Code sections 630 and those following it, especially section 632, make it a crime to record a conversation without the other party's consent whenever there is an expectation that the conversation is private or confidential.
Employment / Labor Attorney
The law differs from state to state, and the issue is whether you need the other party's consent to record. Under federal law, you need only one party to consent. Because you are a party, you may generally record conversations without the other persons knowledge under federal law. Some states require two party consent or have other stipulations and restrictions. Wisconsin, where I practice, is a one party consent state. I'm not a California lawyer, so I can't answer your question definitely. The website I've linked lists California as a two party consent state. Contact a California lawyer to be sure.