Is it permissible to keep money taken surreptitiously from the employer – who did not pay the due wage – in exchange for the wage, or to give it to another worker who has a due wage that the employer did not pay?

If the café owner withholds your rightful wages, and you are unable to obtain them through conventional means, and some of his money comes into your possession, it is permissible for you to take your due from this money. Anything exceeding your due must be returned to him, even through indirect means, and do not give it to any of his other employees. As for the wages of a minor, his guardian must collect them. It is not permissible to dispose of any amount exceeding your right from the man's money, due to the Almighty's saying: "You do not wrong, and you are not wronged," and the Prophet's (PBUH) saying: "There shall be no harm or reciprocating harm." This is what jurists call the issue of "al-Zafar" (gaining possession).