Politics cannot be a winner through political crossovers, said SJB general secretary Ranjith Madduma Bandara.
He is reacting to a decision by MP P. Harrison to leave the SJB and support president Ranil Wickremesinghe.
A vice-president of the party, Harrison said he would unconditionally support Wickremesinghe at the next presidential election.
Around 100 Pradeshiya Sabha members will join him in supporting the president in another two weeks, he told the media in Anuradhapura, adding that a majority in the SJB will follow suit soon.
Harrison said further that he would not expect positions or privileges by doing so, and noted that he had previously been an active member of the UNP for nearly 40 years.