The proposal to amend the Colorado constitution to change the state’s flat rate into a graduated income tax came in under the wire Monday, the deadline for groups to turn in petition signatures for November’s ballot, setting up a high-stakes battle over revenue.

Backers of the graduated tax proposal — which would marginally decrease the tax liability for the lower ends of the new bracket, while raising taxes for others — turned in 157,000 signatures with about an hour to go before the 5 p.m. deadline.

The proposal, if approved at the ballot box, is expected to generate $2 billion more in tax revenue for the state.

Dozens of volunteers and coalition members walked the three blocks from the offices of the Bell Policy Center to the Secretary of State’s office, waving signs and c