If the prices on the menu are the same, but there's a note at the bottom of the menu saying "additional 10% fee to support our workers' healthcare" (or something similar) they are technically telling you, but this is certainly misleading (possible to miss the note, and it's harder to do math) and is very annoying. I've noticed several restaurants doing this. The new CA law explicitly bans this practice.

If the prices are the same and you aren't notified until you get the bill, this is highly unethical and IMO fraud. There's a restaurant near me that does this; they offer to remove the fee if you notice and complain, but also try to guilt you into paying. The new CA law bans this too.

No, a restaurant can charge whatever it likes. What’s fraud is if the menu says an orange juice is $3 but then when the bill comes it’s $3.30 because there’s a 10% healthcare fee the restaurant didn’t list on the menu.

If the restaurant did list the fee on the menu, it’s a gray area. Depends on how prominently, etc. In any event a dark pattern.

If the prices include the 10% increase and there’s a note that says prices were recently increased to cover healthcare, again perfectly ok. Good even.

If they expect customers to magically know about the extra fee ahead of time, and add it to the bill after the meal, it is undisclosed.