New York City Mayor Michael Bloomberg will donate up to $500,000 of his own money to support California’s tobacco tax measure, known as Proposition 29. He challenged supporters to match that amount, according to the Los Angeles Times.

California will vote on the measure June 5. Proposition 29 would add $1 to the price of each cigarette pack, to raise money for research on tobacco-related illnesses and smoking prevention and cessation programs.

Tobacco companies are spending millions of dollars to oppose the measure.

“Every day, tobacco kills. Right now, big tobacco is pouring tens of millions into California to defeat a common-sense measure that would help reduce tobacco use, and something has to be done about it, so I’m making a $500,000 donation to stand up to Big Tobacco, pass Prop 29, and help save lives,” Bloomberg said in a statement.

Proponents of the tax say it is expected to raise more than $800 million for research on tobacco-related diseases and prevention programs. They estimate the tax raise will prevent 220,000 young people from starting to smoke, and encourage 100,000 smokers to quit.

So far, Philip Morris USA and RJ Reynolds Tobacco, two of the nation’s biggest tobacco companies, and their affiliates, have spent more than $30 million against the proposal. In addition to criticizing it for not including funds for treatment, they have attacked the initiative for allowing the proceeds of the tax to be used out of state.

Supporters of the measure have raised $4 million. One backer of the proposal is seven-time Tour de France winner and cancer survivor Lance Armstrong, whose Livestrong Foundation contributed $1.5 million to the campaign. Other supporters include the American Cancer Society and the American Heart Association.