Citing "league sources" it did not name, the Web site said Cavs owner Dan Gilbert has hired a law firm to investigate his suspicions that Heat President Pat Riley and star player Dwyane Wade talked to James about joining them well before the July 1 start of the NBA free agency period.
The Heat signed James and former Toronto forward Chris Bosh prior to the start of the 2010-11 season in an unprecedented assembling of NBA free agent star power.
Gilbert blasted James as a "traitor" for leaving the Cavaliers, and has since poured several hundred thousand dollars into a probe he hopes will convince NBA Commissioner David Stern to investigate alleged tampering, Yahoo! Sports reported.
The Web site said Gilbert is concentrating on an alleged Riley-James meeting in Miami in November 2009 and a meeting of James' representatives with Wade in Chicago in June 2010.
The report came a day before James was to make his much-anticipated first visit to Cleveland since joining the Heat.