We have a project that technically would have been prevailing wage work, but the GC offered to do the work at no cost to the city to gain more city business. Since the city of Irvine technically didn’t hire anyone for the job, would we still be able to file a stop notice for this site?
That's a really interesting situation. If the contractor wasn't actually hired to do the work, and if they aren't being paid by the city, then I don't think that a stop payment notice or a payment bond claim would be available to secure payment. Stop payment notices generally freeze funds that a public entity would pay their contractor with - so I'm not sure there'd be any payment to stop there. And, if there's no formal relationship between the contractor and the city, it seems unlikely that the job would be bonded. Still, contacting the contractor to inquire about a potential payment bond might be a good idea.
If stop notices or bond claims aren't avalable, then standard legal remedies - like breach of contract claims, claims under the state's prompt payment laws, etc. - might be the best bet for payment if a full-blown dispute breaks out. But, before things get to that, sending invoice reminders and demand letters could help to get paid. More on those tools here: (1) How Invoice Reminders Help Contractors Get Paid Faster; and (2) Construction Demand Letters – How To Write One That Gets You Paid.
Considering this is a high profile project, and considering the uniqueness of this situation, it might be wise to consult a local California construction lawyer. If that becomes necessary, you can find the right lawyer here: Top California Construction Lawyers.