Because there was a general election in 2015 and the current parliament hasn't run for it's full term, Theresa May's decision to call a general election on the subject 8th June has to be confirmed by a two thirds vote of MPs.
Parliament confirmed the decision with a vote of 522 in favour, 13 against, and a handful of abstanees.
A massive endorsement.
"I used to believe that anything was better than nothing. Now I know that sometimes nothing is better." - Glenda Jackson