McCollum filed a lawsuit against Expedia and Orbitz, claiming, "they're pocketing the difference as a profit," The Miami Herald reported Wednesday.
"The online travel companies are taking the money that's really owed to the state of Florida," he said.
The suit accuses the companies of paying sales tax on the wholesale price, rather than the retail price of a room.
In Florida, the difference could add up to hundreds of millions of dollars, the newspaper said.
A spokesman for the Interactive Travel Services Association Andrew Weinstein said, "we're very disappointed that the attorney general would align himself with the plaintiff's attorneys making these false claims."