Sitiveni Halapua, Sione Taione, Semisi Tapueluelu and Sunia Fili will not stand for the Democrats after a party committee chose not to select them as candidates for November's election.
Dr Halapua says the reasons for non-selection appear to be specific to each of the four.
He says in his case, his differences with the party have been evident for two years and stem from ideaological divergence.
Dr Halapua says he wants to focus more on addressing what he calls Tonga's development crisis.
"There were a lot of concentration and focus on the struggle for democracy, as a result of which some of the development issues were neglected, as a result of which we are now facing very, very serious challenges and crisis particularly in the area of education and health."
Sitiveni Halapua says he will contest the election as an independent.