Indian politicians are trading barbs over a media report that Facebook Inc's content policies favoured Prime Minister Narendra Modi's party, putting the social network at the centre of a political storm in its biggest market by users.

Lawmakers of Modi's Bharatiya Janata Party (BJP) have accused the social media giant of censoring nationalist voices, after the opposition Congress seized on a Wall Street Journal report to seek a parliamentary investigation of Facebook employees' alleged ties with the ruling party.

Facebook was already a "Left-Congress-leaning platform," said BJP lawmaker and former minister Rajyavardhan Singh Rathore. "This storm in a teacup is merely an exercise to browbeat Facebook for 'allowing' certain opinions to even exist," Rathore wrote in a column in the Indian Express newspaper.

"There are examples of current and former Facebook executives with links to the former government and opposition parties, and some of them have been openly critical of the prime minister as well. To accuse them of being pro-BJP is laughable."

Tejasvi Surya, another BJP lawmaker and a member of a parliamentary committee on information technology, said many people had complained to him that Facebook was "unfairly censoring many nationalist, pro-India or pro-Hindu voices", and that he would take up the matter with relevant authorities.

On Sunday, the Congress party said on Twitter, "Millions of Indians are controlled and manipulated by BJP through Facebook," and its popular messenging service, WhatsApp.

The WSJ report said Facebook's top public-policy executive in India, Ankhi Das, had opposed applying its hate-speech rules to a member of Modi's party and at least three other Hindu nationalist individuals and groups "flagged internally for promoting or participating in violence".

The Journal also said Das had told staff members that punishing violations by politicians from Modi's party "would damage the company's business prospects in the country".

Facebook, which has more than 300 million users in India, referred on Monday to a weekend statement that said it prohibited hate speech irrespective of one's political position but acknowledged, "There is more to do."