A Denver judge is expected to rule Tuesday on the validity of a ballot question seeking to raise Colorado residents' income taxes to benefit public schools.
Opponents of Amendment 66 say they have identified enough suspect petition signatures to call the measure into question. They made their case during a hearing in Denver District Court last week.
The school tax proposal has already been printed on ballots for the Nov. 5 election, but if the tax opponents prevail, votes on the issue won't be counted.
The measure would raise about $950 million a year.
If passed, the additional income tax money would be spent on expanded access to free preschool and other upgrades.
Opponents say the overhaul doesn't make the right kinds of changes to improve schools.