The best weapon to use against greedy corporate giants is ridicule, as Groucho Marx did with Warner Brothers. Here's the Wikipedia version of the story surrounding the Marx Brothers film A Night In Casablanca:
A popular myth (spread in part by Groucho himself) surrounding the movie is that the Marx Brothers were threatened with a lawsuit by Warner Bros. for the use of the word "Casablanca" in the title, it being an infringement on the company's rights to the 1942 film Casablanca. Groucho responded with a letter asserting that he and his siblings had use of the word "brothers" prior to the establishment of Warner Brothers (and many others had before that), and often the story is told that Groucho threatened a counter-suit based on this assertion. He also mentioned that he would consider further legal action by pointing out to Warners that the title of their current hit film Night and Day infringed on the titles of two Marx Brothers films; A Night at the Opera and A Day at the Races.
The true story is that the original storyline for the Marx film was intended to be a direct parody of Casablanca, with the characters having similar sounding names to the characters and actors in the 1942 film. Groucho Marx has said that an early draft named his character "Humphrey Bogus", a reference to the leading actor in Casablanca, Humphrey Bogart. Warner Bros. did not actually litigate, or even threaten to litigate, but it did issue a formal inquiry to the Marx Brothers concerning the plot and script of the film.
The Marx Brothers exploited the situation for publicity, making it appear to the public that a frivolous lawsuit was in the works, and Groucho sent several open letters to Warner Bros. to get newspaper coverage. These letters were among those he donated to the Library of Congress, and he reprinted them in his book The Groucho Letters, which he published in 1967.
In the end, the matter died without legal action, and the storyline of the film was changed to be a send-up of the genre rather than Casablanca specifically. Warner Bros. now owns the distribution rights to this film via Castle Hill Productions.