One of the world's richest men has decided to roll into a political battle over whether Florida should legalize medical marijuana.

New campaign finance reports filed Tuesday show that billionaire casino magnate Sheldon Adelson is now helping the group that wants to defeat the constitutional amendment that will be on the November ballot.

Adelson, a high-profile Republican donor and CEO of Las Vegas Sands Corp., wrote a single check for $2.5 million to the political committee trying to defeat Amendment 2. It represents nearly all of the $2.7 million raised so far by the Drug Free Florida Committee.

Adelson and his company have been trying to expand casino gambling in Florida only to run into opposition in the Florida Legislature. Legislative leaders and other top Republicans in Florida are opposed to the medical marijuana amendment even though polls have consistently shown a majority of voters support the measure. Adelson's wife is a physician who helped found drug-abuse treatment centers.

A spokeswoman for the Drug Free Florida Committee said she could not say why Adelson is donating to the group.

But Sarah Bascom did contend that opponents "vow to keep raising money so that we can continue to ask the hard questions of the amendment's supporters and inform Florida voters on the real issues behind Amendment 2."

Bascom's group maintains that the medical marijuana measure has a loophole that will allow people to obtain marijuana for nearly any reason. Supporters say that is not true, and note the Florida Supreme Court rejected a similar argument made by Attorney General Pam Bondi.

Ben Pollara, campaign manager for United for Care, labeled Adelson an "out of state gambling interest." Pollara said many of the organizers opposing the amendment are not "credible people" to argue that "medical marijuana is bad for the people of the state of Florida." The group pushing the amendment has been largely backed by trial attorney John Morgan. Former Gov. Charlie Crist, who is running against incumbent Gov. Rick Scott, works at Morgan's firm.

Pollara did acknowledge that Adelson's financial support was unexpected, but he remained confident that Floridians would continue to support the amendment.

Sixty percent of voters need to vote yes on the amendment in order for it to pass.