Proponents of the measure, however, argue that it would not only help California's sizable budget deficit but would in turn reduce crime by shifting law enforcement's focus to harder substances and targeting only serious offenders.
The California government has projected that at an excise tax of $50 per ounce, the new law would bring in about $1.4 billion in additional revenues. It would save the state $960 million a year in enforcement costs, according to the Cato Institute.
"We are looking at about $12 million in revenue [a year]," said David McPherson, an Oakland revenue and tax administrator. "We recently laid off 80 cops and this community would love to have those 80 cops back."
Proposition 19 has earned the endorsement of several influential groups, including the California chapter of the NAACP, Latino Voters League, and the Service Employees International Union and the United Food and Commercial Workers.
And former U.S. Surgeon General Joycelyn Elders has defended the measure, saying that much more harmful substances, such as tobacco and alcohol are legal, and marijuana should be not be treated differently.
Tom Angell of Yes on 19 said his organization had conducted internal polls that put the ballot measure ahead, with 56 percent in favor and 41 percent opposed, but that regardless of poll results the race was really close.
Yes on 19 released its first TV ad today that features former San Jose Police Chief Joseph McNamara discussing the bill's public safety aspect. Angell said that his group was doing everything possible to get the message out to voters and let them know that it was possible to change the laws to end prohibition.
"I don't know why our opponents are trying to nitpick this measure," he said. "They seem to have such little faith in local officials to handle this."
Angell said he hoped that when voters entered the privacy of a voting booth, they will vote yes. Carla Marinucci, the chief political writer for the San Francisco Chronicle, said the measure's passage was possible.
"Behind the scenes, people were saying I'm not gonna vote for this," she said. "But there is a lot of support for marijuana in this state."
ABC News' Huma Khan contributed to this article.