In the Star Trek franchise shows Star Trek: The Next Generation, Star Trek: Deep Space Nine and Star Trek: Voyager, each show almost always had 26 episodes per season. Besides Voyager's first season, the only exception in this is the second season of Star Trek: The Next Generation, which instead had 22. Why is this?
Because of the 1988 Writer's Guild of America Strike. Technically it occurred at the very end of the previous season, but the next season was impacted more heavily because the producers weren't able to consult with the writing team on the upcoming scripts.
Extensively discussed in this series of interviews:
There was a writers' strike in 1988.
The Writers´ Guild of America went out on strike in the spring and summer of 1988. They demanded more creative control and residuals for the shows they wrote.
The writers of ST:TNG at Paramount joined in despite their Sacred Duty.
The strike ended on August 7, but the production pipeline was adversely affected, and ST:TNG wasn't able to start airing until November 21. (This episode, "The Child", contained the first appearance of Whoopi Goldberg playing Guinan.)