A lawsuit filed Wednesday challenges a ballot measure that would scrap Colorado's winner-take-all system for Electoral College (search) votes and award them based on how well the candidate did in the statewide popular vote.

The lawsuit filed by Jason Napolitano (search) asks a federal judge to declare the closely watched proposal unconstitutional before the Nov. 2 vote. Napolitano, who describes himself simply as a registered voter, said it is up to state lawmakers to determine how electoral votes are distributed.

Amendment 36 (search) has drawn national attention in part because the race between President Bush and Democratic challenger John Kerry is expected to be close. The plan would apply to this year's election, meaning that Bush or Kerry could win the statewide vote but receive only five of Colorado's nine electoral votes.

Supporters say the proposal would make sure every vote is represented. Critics say it would make Colorado politically irrelevant because only one electoral vote would be up for grabs in most elections.

Napolitano said the repercussions have not been fully discussed and that applying the plan retroactively violates federal law.