The state Senate has endorsed a bill to allow NorthWestern Energy to buy an additional portion of a coal-fired power plant in eastern Montana for $1 without the approval of state utility regulators.

The Senate voted 32-18 in favor of the bill Wednesday. It faces a final vote before moving to the House.

Supporters say the bill takes advantage of other states' decisions to quit using coal power and prevents opponents of coal-based energy from challenging the issue before the Public Service Commission.

Opponents say the PSC should have to approve of the purchase.

Colstrip's two older units are scheduled to shut down by mid-2022 under a legal settlement. The bill seeks to extend the life of the plant's two newer units as other Colstrip co-owners look at reducing their use of coal energy.