The secretary of state reports that with 400,000 ballots outstanding, the measure that would add a $1-a-pack cigarette tax is trailing by 17,500 votes.
Since June 5, the measure known as Prop 29 has trailed in vote counts by less than a percentage point.
Through a barrage of campaign ads, tobacco companies were able to cut support for the plan from a two-thirds majority in March to a dead heat on Election Day.
Opponents of the measure raised $47 million to fight it, dramatically outspending supporters, who raised $12 million.
Election officials have until July 6 to report final results.