Any dissimilar treatment to the secular organizations is unconstitutional. Like schools, sometimes public libraries have policies prohibiting use of facilities for religious or political meetings. These policies are unconstitutional. The basic constitutional principle is simple. If a public institution opens up its facilities to use or rent by outside secular organizations, the same institution must open its facilities to religious organizations, including churches, on a nondiscriminatory basis.
Any discrimination whatsoever violates the constitutional guarantee to freedom of speech.
Equal access means equal treatment. Any discrimination is unconstitutional. Religion is not a disability. Whenever government makes you take the back seat of the bus because of your religious faith or practice, the government must be challenged and its practice must be altered.