I've not looked in to that one.
I've mainly heard of his arguments over the employment of his girlfriend and future wife and him writing lyrics for the theme song to steal monetization of it, and him interfering with later movies and TNG.
Yeah, he wrote lyrics for the TOS theme so he'd get half the writer's royalties. He was sleeping with Majel Barret while still married to his first wife, and established the licensing company he founded in Barret's name so when he divorced his first wife she wouldn't get a share of it. He screwed Dorothy Fontana out of a raise during the production of TAS, and she was very reluctant to work on TNG as a result (Shatner did a documentary about the first two years of TNG called Chaos on the Bridge and it's amazing).
During the pre-production period on TMP, when it was moving back and forth between being a movie, a TV show and a TV movie, he played a lot of power games to try and gain creative control and the sole production credit. He was eventually successful but it delayed the movie entering production by about a year. He had a severe case of writer's block during the filming, leading to two production halts because they ran out of script to shoot. Shatner, Nimoy and Robert Wise had script consult rights, but when they made suggestions throw tantrums and pick fights. Eventually Paramount removed him from the production and Shatner, Nimoy, Wise and Howard Livingstone completed the script.
He wasn't the only reason TMP was a production nightmare that came this close to bankrupting Paramount, but he was a big part of it. Memory Alpha's writeup of the production is fascinating.
