Facebook co-founder Sean Parker is giving $100,000 (£62,640) to the push for the legalisation of cannabis in California. Campaigners had complained they were short of cash in the run-up to a vote on the measure on 2 November.

His contribution follows two donations by his fellow co-founder, Dustin Moskovitz, totalling $70,000. Polls suggest voters will approve legalising cannabis. A survey by Public Policy Polling last monthfound 47% for and 38% against.

The ballot coincides with mid-term elections for a new California governor as well as Congress. Legalisation could take effect the day after the ballot, making California the first state in the US to do so.

Parker, 30, founded the music-sharing site Napster when he was 19 and went on to raise funds for the social networking site Facebook, becoming its first president. He has since left the company, though he retains a stake and is worth millions. His donation was listed this week in filings issued by the campaign for Proposition 19, also known as the Regulate, Control and Tax Cannabis Act of 2010. Parker has made no public statement about the donation.

Stephen Gutwillig, a spokesman for Drug Policy Alliance, which is spearheading the legalisation campaign and is the main beneficiary of the donation, told Associated Press: "What's interesting here is that [Parker] is a member of the generation that really gets it. We think he's pivotal to the future of drug policy reform in the country."

Others say cannabis is much stronger than it was in the 1960s and 1970s and is dangerous, impacting on the health services and the workplace

In an ironic twist, advocates of reform have complained of a ban by Facebook on adverts supporting Proposition 19. Facebook has responded that company policy only prohibits images of drugs, and not adverts either in favour or against legalisation.