Facebook's India executives are being grilled by a parliamentary committee over allegations of political partisanship and hate speech.
The social media giant is accused of going easy on ruling BJP supporters who allegedly violated hate speech rules.
But the BJP is also irked with Facebook - it has accused it of bias against Prime Minister Narendra Modi.
The company denies the allegations, but the row puts it in a precarious position in its biggest market.
The app is hugely popular in India, with more than 300 million users - and so is its messaging platform, WhatsApp, which has 400 million users.
Details were unlikely to emerge immediately as the parliamentary committee session is a closed-door hearing.
The allegations first appeared in a report by the Wall Street Journal (WSJ) last month. The company insists that it doesn't allow hate speech on its platforms.
"We prohibit hate speech and content that incites violence and we enforce these policies globally without regard to anyone's political position or party affiliation," Facebook told the BBC in an email recently.
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But the WSJ investigation immediately sparked calls for an inquiry, leading to Wednesday's parliamentary hearing. Facebook's head of business for India, Ajit Mohan, is expected to appear before the 30-member committee.
The committee has members from all political parties but it is led by Shashi Tharoor, an outspoken MP from the main opposition Congress party.
The closed-door hearing will cover Facebook policies on "safeguarding citizens' rights" and preventing the "misuse of social/ online news media platforms" among other things.
What are the allegations against Facebook?
The company is accused of allowing anti-Muslim rhetoric and other content on the platform, in what the WSJ said was favouritism towards the Bharatiya Janata Party (BJP).
The report said that Facebook deleted some anti-Muslim posts by a BJP lawmaker only after the paper asked about them. It also alleged that similar posts by at least three others, who supported the BJP, were not taken down even after they were flagged for violating the company's hate speech rules.
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