Senior PTI leader Senator Azam Khan Swati was arrested before dawn on Thursday.
It is learnt that he was taken into custody by the Federal Investigation Agency (FIA) from his home in the federal capital.
The PTI lawmaker was arrested over his alleged controversial tweets after a case was filed by the agency’s Cybercrime Wing (CCW) late Wednesday night.
Azam Swati has been accused of making statements against institutions and inciting people.
He is the third senior leader of the Imran Khan-led PTI who has been arrested by the FIA after Saifullah Khan Nyazee and Hamid Zaman. However, Nyazee and Zaman are being probed for their alleged involvement in the prohibited funding to the party.
Confirming the development, PTI Secretary General Asad Umar condemned the move and demanded that Swati be released immediately.
The PTI has often been accused by the government functionaries of using social media against state institutions and running smear campaigns.
In August, a report on negative propaganda against the army on social media following the Lasbela helicopter crash discovered 178 accounts linked to the party.
After an investigation, social media activists and their handlers were tracked down, according to sources.
More than 2,350 posts were made through 580 accounts, and the campaign also included 18 Indian accounts. According to sources, cases will be filed against the accused under the relevant laws.
After an Army aviation helicopter went missing in Lasbela during a relief operation in flooded areas, a smear campaign was launched against the Pakistan Army, according to the report.
PTI social media activists, on the other hand, have apologised for their actions, it added.