That’s not why it’s unconstitutional, but it’s unconstitutional. Violates 14th amendment equal protection among other things, but not right to assembly, which is about political gatherings.
The right to assemble is NOT limited to political gatherings.
“...or the right of the people peaceably to assemble....”
There are NOT restrictions (such as political gatherings) on the right. Assembly includes church gathering, unions, political rallies, business, family gathering, etc.