Nevada Gov. Joe Lombardo (R-NV) is warning that California’s climate policies could have ripple effects beyond its borders, cautioning that changes to the state’s oil regulations may threaten fuel supplies across the West.

In a letter dated Monday to California Gov. Gavin Newsom (D-CA), Lombardo expressed concern about proposed changes to the state’s cap-and-trade framework being considered by the California Air Resources Board. He urged his Democratic counterpart to ensure regulators consider how the policy might affect neighboring states that rely on California’s refining network.