TORONTO -- A Toronto-based law firm has launched a proposed class-action lawsuit against Ticketmaster, alleging the ticket-selling giant has been taking "double-dip commissions" on the resale market for years.

Sotos Class Actions accuses Ticketmaster of allowing professional resellers to buy "massive volumes" of tickets to concerts and other events, then resell them on the secondary market "at significant markups."

In a statement of claim filed to the Ontario Superior Court of Justice on Wednesday, Sotos says the company turned a blind eye to resellers' use of so-called "bot" software to gobble up tickets.

It says this allowed Ticketmaster to increase its profits by taking commissions on both the original sale and the resale.

None of the allegations contained in the statement of claim have been proven in court and Ticketmaster has not filed a statement of defence. The company did not immediately respond to a request for comment.

The lawsuit seeks $250 million in damages.