Is it permissible to work in a government institution that levies taxes on transport vehicles, and is it permissible to accept gifts from its employees?

It is permissible to work in a federal institution and accept gifts from its employees if registration therein is optional and participants pay taxes by their own choice, or if it is mandatory imposed by a just ruler for the public good. However, if the institution exists to achieve private interests and people are unjustly forced to register and pay taxes, then it is not permissible to work there, so as not to assist wrongdoers, nor to accept any gift from the salary of such forbidden work. This is based on the Almighty’s saying: "And cooperate not in sin and aggression. And fear Allah; indeed, Allah is severe in penalty."