If it passes, it would be the biggest change ever in how a state votes for president. The issue: Should Colorado abandon the winner-take-all system and divide up electoral votes based on the popular vote?
Supporters say the current system doesn't reflect how people actually vote.
"The entire state of Colorado is not voting for one person," says Julie Brown, who supports the amendment. "If you were giving away one electoral vote, the current system would make sense."
If it passes, Colorado would split its nine electoral votes, according to each candidate's state vote percentage. And that could change who gets elected president.
Here's why. It takes 270 electoral votes to win. If there's a close vote in the rest of the country and, say, candidate A got 267 electoral votes and candidate B, 262, then under the current system, if candidate B wins Colorado, he wins all its nine electoral votes and the White House.
But, if the Colorado vote splits five to four, candidate A would pick up four of those nine votes, making him the winner.
What's more, if this proposal passes in November, it would count for the 2004 election.
If Colorado had used this system four years ago, Al Gore would now be president.
But opponents say the plan would diminish the value of Colorado to the candidates, since the prize would no longer be all nine votes.
"It would take Colorado and use us as political lab rats in the whole effort to reform the Electoral College," says opponent Katy Atkinson. "They want Colorado to step back and marginalize itself on the national political scale."
Republicans in Colorado, who have a slight edge and could stand to lose the most, generally oppose it.
But politics aside, there's a big legal question that could end up at the Supreme Court. The U.S. Constitution says a state's legislature must decide how to tally its own electoral vote.
But this change would be made by voter initiative, not the legislature.
"I'm sure the last thing the country or the Supreme Court wants is to get in the middle of another election dispute," says election law expert Richard Pildes. "But on the other hand, this is really a basic constitutional question that the federal courts would undoubtedly have to step in and answer."
If the measure passes, the drawn-out legal battles it spawns could make Colorado the "Florida" of 2004.