A same-sex marriage ban prevents governments and universities in Michigan from providing health insurance to the partners of gay workers, the state Supreme Court ruled Wednesday.

The 5-2 decision affects up to 20 universities, community colleges, school districts and governments in Michigan with policies covering at least 375 gay couples.

Gay rights advocates said the ruling was devastating but were confident that public-sector employers have successfully rewritten or will revise their benefit plans so same-sex partners can keep getting health care.

The ban, a constitutional amendment approved in November 2004, says the union between a man and woman is the only agreement recognized as a marriage "or similar union for any purpose."

The court ruled that while marriages and domestic partnerships aren't identical, they are similar because they're the only relationships in Michigan defined in terms of gender and lack of a close blood connection.