India's Madison Communications is asking a court to quash an antitrust investigation into the advertising agency, arguing its executives were unlawfully questioned during March raids without an attorney present, court papers reviewed by Reuters show.

Madison was among numerous ad agencies and a group of broadcasters raided by the Competition Commission of India (CCI) on suspicion of collusion over advertising rates and discounts, in the country's strictest regulatory action on the sector to date. Other agencies raided include global giants WPP's GroupM, Dentsu, Publicis and Omnicom.

The legal action filed by Madison with the High Court of Delhi on October 8 is the first to seek to have the probe into one of the agencies halted.

According to the 276-page court papers filed on October 8

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