Health cooperatives are collapsing at such a rapid clip that some co-ops and small insurers are forming a coalition to consider legal action to try to change health-law provisions they blame for their financial distress.

Colorado’s co-op and one in Oregon announced Friday that they were folding, joining six others that have already collapsed or said they will unwind operations. The eight co-ops have received nearly $900 million in federal funds that may not be paid back.