A report released Monday by the Treasury Department found that prices of government-backed cryptocurrencies are mostly set by market speculation and don’t have much economic reality underpinning them. As such, they could threaten the stability of the U.S. financial system if they become too entwined with the mainstream financial system, the report warned.

“Crypto-asset prices appear to be primarily driven by speculation rather than grounded in current fundamental economic use cases, and prices have repeatedly recorded significant and broad declines. Many crypto-asset firms or activities have sizable interconnections with crypto-asset entities that have risky business profiles and opaque capital and liquidity positions,” the report from the Treasury found.