Can an employee get what’s owed him by cheating?

There is an employer whose workday is 9 hours. However, he pays for vacations and sick days as if the workday were only 8 hours (which is against the law; the law states that the employer has to pay according to a regular workday). There was no special agreement of any kind with the employer that he was going to pay vacations and sick days in any irregular way. Can an employee report working 8 hours, when in fact she only worked 7, in order to compensate herself for the pay that’s owed her? Is this considered a case where one can take justice into his own hands?

If all the women who work for this employer know that this is the way he pays vacations and sick days, then she doesn’t have any valid arguments against him. If the worker did not know about this arrangement, then she can take justice into her own hands only on the first month of work, because she can argue that she didn’t know that she was going to be taken advantage of this way. Starting next month, however, she can no longer claim that she didn’t know. If she stayed at this place of work anyway, that constitutes an implicit agreement to these conditions. And if this arrangement is mentioned in the contract that she signed with her employer, then she is obligated to accept this pay, even if signing such a contract was illegal.   

Shulchan Oruch, section Choshen Mishpat, chapter 331