IN connection with a number of petitions challenging the election of Shiv Sena candidates under the Representation of People's Act, party chief Bal Thackeray has been sent notices to show cause why he should not be named a collaborator in corrupt practices. It began with the case of Ramesh Prabhoo, whose election to the Vile Parle assembly constituency in Mum-bai in '87 was challenged by the losing Congress candidate.