This “slap on the wrist” handling of it is way too lenient and can only apply to people who accidentally underpay workers. If you can somehow prove that an employer does it on purpose or rejects a person’s claim for their salary they should be held accountable and be put in the same category as stealing a car with up to 4 years imprisonment.

If you only make employers pay a fine and backpay to whoever requests it might be less than the amount they stole. This way optimal business strategy become “get insured for it and continue”.