The issue, however, prompted the Opposition, including the DMK, to question why police were not acting against BJP leaders H Raja and S Ve Shekher who are also facing a number of cases.
Karunas, also a well-known actor and founder of a small outfit, was picked up from his house this morning by a special team, police said.
At a recent public meeting Karunas had reportedly made some remarks in relation to Chief Minister K Palaniswami and the police, besides some alleged caste related ones, drawing criticism from various quarters.
The actor, who aligned with AIADMK for the 2016 Assembly polls, was elected from Tiruvadanai constituency in Ramanathapuram district on an AIADMK ticket.
He had later met sidelined AIADMK leader and RK Nagar MLA TTV Dhinakaran, who has also floated his own Amma Makkal Munnetra Kazhagam (AMMK), post his ouster from the AIADMK.
Responding to the police action against him, Karunas said he was not aware whether the Speaker P Dhanapal's approval was taken prior to his arrest as is the requirement and charged the government with "denying freedom of expression."
"I am ready to face the matter in the court," he said.
DMK President MK Stalin as well as Dhinakaran said Karunas could have avoided making such remarks but wondered why Raja and Shekher have not yet been arrested.
There was no doubt that elected representatives should "not exceed their limits" and they had the duty of ensuring public peace and harmony, Stalin said in a statement.
Karunaas had, however, expressed regret for his utterances, the DMK Chief said and sought to know why the MLA was still picked up.
"The rule of law is being selectively implemented in Tamil Nadu. Raja, who threatened to damage statues of (rational leader EVR) Periyar and one who demeaned and defamed police, besides making remarks against spouses of temple administration staff, has not yet been arrested," he said.
Stalin, Leader of Opposition in the state Assembly, said Raja was still attending public events with police protection and asked why another BJP member, Shekher, was also still not arrested in connection with a case of making demeaning remarks against women journalists.
"There is one rule for Karunas and another for Raja and Shekher and this is an injustice. This attitude of the AIADMK government is condemnable," he added.
Dhinakaran also said it was "wrong" on the part of Karunas to have made such remarks "emotionally" and regretted that his "friend" has been arrested.
He also sought to know why the K Palaniswami government was yet to act against Raja.
"The government and police should take a consistent stand. Raja is making so many remarks. He spoke against the police and juiciary. The police department just filed a case against him and has gone silent," he said.
DMDK founder Vijayakant 'condemned' the arrest of Karunas and asked why "some other persons freely airing their views" were not facing action, apparently referring to Raja.
Meanwhile, at a meeting of its State Council, the CPI (M) adopted a resolution on this matter, saying the AIADMK government had become a "puppet" of the Centre.
While the remarks made by Karunas can be "critiqued," why has the police not acted against Raja? it asked.
It also referred to the police action against a woman research student who raised anti-BJP slogans against party's state unit chief Tamilisai Soundararajan in a Tuticortin-bound flight recently.
It sought the immediate arrest of Raja.