Mr Khera was on Thursday arrested by the Assam Police at the Delhi airport.
Congress general secretary Jairam Ramesh on Thursday called police action against party spokesperson Pawan Khera a new example of Prime Minister Narendra Modi's politics of "vendetta, harassment and intimidation."
The Bharatiya Janata Party (BJP) was worried due to Congress's successful Bharat Jodo Yatra, and now it is scared of the 85th plenary session of the Grand Old Party which will start from Friday, he told reporters here.
The BJP also tried to detail the plenary session, he alleged, referring to the Enforcement Directorate's recent raids on Congress leaders in Raipur, and Khera's detention on Thursday.
Freedom of speech is under threat, but more importantly freedom after speech is also under threat, Mr Ramesh quipped.
Talking about opposition unity, Mr Ramesh said it would be strengthened when the Congress becomes strong.
Mr Khera was on Thursday arrested by the Assam Police at the Delhi airport after he was deplaned from a Delhi-Raipur flight in connection with alleged derogatory remarks against the prime minister.
Mr Khera had recently called him "Narendra Gautamdas Modi", in an apparent swipe at the prime minister over the row involving business tycoon Gautam Adani.
The prime minister's full name is Narendra Damodardas Modi, with the middle name standing for his father's name. The BJP accused the Congress spokesperson of insulting the prime minister.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)