All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The interest the government is going to repay along with the taxes unfairly withheld from salaries could be given either as a gift and donation or in the form of obligation:
According to the first probability, it is permissible to take it. But according to the other probability, that it is in the form of obligation under the law of the government, then it should be investigated: if the government has invested the withheld taxes, then it is permissible to take the profits if they came from permissible investments. But if they came from bank interest and the like, then it is not permissible to take it, unless one is needy. However, in case one is not needy, he may take it and spend it on the public benefit of Muslims.
On the other hand, if the government has not invested the taxes, and rather is obliged by law to repay them with interest, then that would be a usurious law. It is possible for him who is given such interest to take it and spend it on the public benefit of Muslims as we have already clarified. If he is needy, then he has the right to take from it according to his need.
Allaah Knows best.