A ballot measure to create a graduated income tax system in Colorado has a slight edge over an opposing proposal to maintain the state’s flat tax as of 9:20 p.m., according to early results from the Colorado Secretary of State’s Office.

Amendment 87 — which would replace Colorado’s flat income tax with a graduated system — was passing with about 50.5% of the vote. “Yes” votes, 992,655, outnumbered “No” votes, 972,156, which is a 20,499 vote margin.

Proposition 136, which would cap the state’s income tax at its existing rate of 4.4%, was failing by a slight margin, with support accounting for just 47% of the vote. “No” votes, 1,024,332, were leading “Yes” votes, 911,794, which is a 112,538 margin.

Both ballot measures require a simple majority to pass.

Colorado is one of 15 states with a flat tax rate. The federal government, as well as 27 states and Washington, D.C., use some form of graduated income tax, while eight states have no income tax.

The graduated tax system proposed by Amendment 87 would lower taxes for the vast majority of Coloradans while raising taxes for the top percentage of earners. It would generate more than $2 billion for the state government to spend on healthcare, education and childcare, according to the official ballot information booklet.

The constitutional amendment was led by the Protect Colorado’s Future Coalition that includes progressive think tanks like the Bell Policy Center and Colorado Fiscal Institute, as well as groups like the Colorado Organization for Latina Opportunity and Reproductive Rights, the Colorado Consumer Health Initiative, the Colorado Cross-Disability Coalition, Hunger Free Colorado, the Colorado PTA and other nonprofits and advocacy groups.

Proposition 136 was brought by Advance Colorado —  a conservative think tank that sponsored nearly half of the ballot measures before voters this election cycle — as a direct countermeasure to Amendment 87.

Pass or fail, Prop 136 would maintain the current flat tax rate in the Colorado Taxpayer Bill of Rights. But if both Prop 136 and Amendment 87 pass, it would create legal questions that would have to be answered by a court, according to the official ballot information booklet.