The Colorado Secretary of State said Friday that supporters of a measure to legalize possession of marijuana for recreational use need an additional 2,500 signatures in order to get the initiative on the ballot.

Seattlepi.com reports that Secretary of State Scott Gessler said tens of thousands of signatures already turned in were invalid. Supporters have about two weeks to collect the new signatures.

The group “Campaign to Regulate Marijuana Like Alcohol” turned in about 160,000 signatures in favor of their proposal last month; only 84,000 are required. The article notes election officials said 80,000 of those signatures were invalid.

Medical marijuana is legal in Colorado. The number of dispensaries has grown, and 80,558 state residents had medical marijuana cards as of November 2011, according to the state Department of Public Health. There is much debate within Colorado about medical marijuana—85 communities in the state have banned or stopped openings of dispensaries.

The Colorado measure would allow adults over 21 to be able to possess small amounts of marijuana without a doctor’s recommendation. Even if the measure is approved, marijuana would remain illegal under federal law, the article notes.

Proponents of marijuana legalization have also submitted signatures for a ballot proposal in Washington state.