Florida voters approved an amendment Tuesday that will block the state’s legislature from expanding sports betting without a referendum, despite opposition from the NFL’s Miami Dolphins, who argued the bill would essentially end efforts to legalize sports wagers.

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Amendment 3, which passed with 64 percent of the vote, mandates that any effort to expand casino-related gambling in Florida will require a statewide vote to pass. The measure drew strong support and financial backing from the Walt Disney Company and the Seminole Tribe of Indians, which operates casinos in the state.

“This amendment ensures that Florida voters shall have the exclusive right to decide whether to authorize casino gambling by requiring that in order for casino gambling to be authorized under Florida law, it must be approved by Florida voters,” the amendment says.

If the amendment had failed, Florida’s state legislature could have sought to legalize sports betting at casinos through a bill, bypassing a vote by state residents. Any effort to implement sports gambling will now require a 60-percent majority vote from state residents.

Ahead of Election Day, the Dolphins urged Florida voters to vote “no” on the Amendment 3, arguing that the measure would “effectively block any chance for legal sports betting in Florida.” Sportsbook operators FanDuel and DraftKings also opposed the amendment.

Several states, including New Jersey and Delaware, have already entered the sports betting market since the U.S. Supreme Court struck down a federal ban on the controversial pastime last May. The court’s ruling allows states to determine whether to legalize sports betting on an individual basis.

Prominent U.S. sports leagues opposed legalized sports betting for decades, but most, including the NBA, NHL and individual NFL teams, have begun to integrate gambling into their events. The NFL has called on Congress to regulate sports betting at the federal level.

A fully legalized, regulated sports betting industry could be worth up to $2.3 billion to the NFL annually, according to a study last September by Nielsen Sports commissioned by the American Gaming Association.