Missouri Gov. Mike Parson is expected to sign into law the state's first gas tax increase in decades.

Parson is scheduled to sign the legislation Tuesday. The law will gradually raise the state’s 17-cent-a-gallon gas tax to 29.5 cents over five years, with the option for buyers to get a refund if they keep track of their receipts.

The first 2.5-cent increase is slated to take effect in October, which will bring the gas tax to 19.5 cents.

A conservative advocacy group’s Missouri chapter is trying to put the gas tax hike to a public vote in 2022.