On the basis of the First Amendment,
as well
as the general principles of the Constitution, he
opposed public payment for chaplains in Congress and the military, spoke out against national proclamations of days of prayer (though
as president he did «recommend» them) and while president vetoed congressional efforts to incorporate churches in the District of Columbia (fullest statement, V: 103 - 105) At the same time, Madison frequently opined that it was appropriate for
private citizens to support chaplains and various kinds of semiorganized public religion through voluntary contributions (V: 104,105)
If they wanted to
oppose it apart from their official office, then they have that right
as a
private citizen, but anything within their capacity
as a mayor is overstepping themselves.