Sued For Making A Counter Strike Map

I'm not familiar with Canadian law but what would you actually sue this guy for? Thanks to Yakk for the heads up.
An independent video game concept designer is in legal trouble for helping to virtually recreate the city's metro system for one of the most popular games in the world. Montreal's public transit authority, the Societe de transport de Montreal (STM), threatened to sue Diego Liatis, 35, if he published his version of the popular game Counter Strike online.