Is the second wife entitled to demand an allowance equal to that of the first wife, knowing that the workplace does not allow the registration of more than one wife, and that the allowance is issued in the name of the first wife?

A husband must be just between his wives regarding the nights spent (lodging) and, according to the more preponderant opinions, regarding maintenance and clothing. This is the choice of Shaykh al-Islam Ibn Taymiyyah, due to the generality of the Prophet's (peace be upon him) saying: "Whoever has two wives and inclines to one of them over the other, will come on the Day of Resurrection with half of his body drooping," and due to the Prophet's (peace be upon him) actions.

Therefore, justice in maintenance between two wives is obligatory, by giving the second wife an amount equal to what the first wife receives, or by making them both partners in what is given.