First of all, it is definitely illegal to work overtime voluntarily. But I'm telling you, it's not that simple Suppose the Labor Bureau accepts: 1, you have to take out the contract you signed with the company. 2, you have to have proof that you usually work overtime. This is not easy to find. Usually it's sign-in, credit card records and so on. If you really want to go to court, you have to secretly take these records and have a salary slip. 3. At present, there are a lot of regulations on this piece in our country, which are also very chaotic. Large companies generally have their own algorithms, and there are generally no particularly big loopholes.
According to your situation, I suggest you get the evidence first and talk to the leader. In your case, I don't think it will be successful or even acceptable if there is no evidence of overtime.