The League of Women Voters is urging Floridians to vote "no" on Amendment 5 on the November ballot.
The proposition would require a two-thirds vote of the Florida Legislature to pass a new tax or increase an existing one.
League President Patricia Brigham says that would make it all but impossible to get rid of tax breaks enjoyed by special interests.
Republican leaders in the legislature who championed Amendment 5 say they want to protect Floridians from future lawmakers who might be more inclined to raise taxes.