Majithia is the kingpin of the drug mafia operating in Punjab, AAP's in-charge of party affairs in Punjab Singh reiterated in a statement here.
The AAP leader said that Majithia may consider himself very "powerful" but he cannot curb his voice by filing defamation case against him.
He said that the drug trade in the Punjab flourished so much in the last almost nine years of the Akali rule that has ruined the future of the youth.
Majithia today filed a case of criminal defemation against Singh in the court of Judicial Magistrate Bikramdeep Singh for alleging that he had patronised the drug mafia.
In his complaint, Majithia, who is also the grandson of former Union minister Surjit Singh Majithia and elder brother of Union Food Processing Minister Harsimrat Kaur Badal, rejected the allegation levelled against him as "baseless". He said that the allegation has damaged his reputation.