Liza Lovdahl Gormsen, a competition law academic and senior adviser to the UK's Financial Conduct Authority (FCA), said she was initiating the case on behalf of consumers in the UK who used Facebook between 2015 and 2019.
TCS's board of directors had approved a buyback offer of up to Rs 18,000 crore, with 4 lakh shares priced at Rs 4,500 each.
In Wednesday's trading session, Vodafone Idea (Vi) shares soared over 10% on the BSE to 13 apiece.