Twitter has been criticised for repeatedly failing to remove anti-Semitic and abusive tweets which were flagged by MPs.
Labour MP Yvette Cooper said it was hard to believe that enough was being done to tackle hate crime, with posts reported months ago still remaining on the platform.
Her comments came as senior figures from Twitter, Facebook and Google faced the Commons' Home Affairs Select Committee, which is investigating how companies are dealing with abusive content.
Ms Cooper, chair of the committee, said no action had been taken against anti-Semitic tweets shown to representatives of Twitter at a previous hearing.
They included abuse directed at Labour MP Luciana Berger, who has been a high-profile target of online trolling, which has already been flagged to the platform twice.
Addressing Twitter's Sinead McSweeney, vice president of public policy and communication for Europe, the Middle East and Africa (Emea), Ms Cooper said: "I'm kind of wondering what we have to do.
"We sat in this committee in a public hearing and raised a clearly vile anti-Semitic tweet with your organisation.
"It was discussed and it is still there, and everybody accepted, you've accepted, your predecessor accepted, that it was unacceptable. But it is still there on the platform.
"What is it that we have got to do to get you to take it down?"
She added: "Part of the problem is, it's like even when we raise it in a forum like this, nothing happens.
"It's very hard for us to believe that enough is being done when everybody else across the country raises concerns."
Ms McSweeney said she did not know why the tweets remained, adding: "I will come back to you with an answer as to why they are still on the platform."
Ms Cooper said her office had also reported a series of violent tweets, including threats against Theresa May, and racist abuse towards shadow home secretary Diane Abbott, which had not been taken down.
She disputed Ms McSweeney's suggestion that offensive tweets would normally be removed from the site within two days of being reported.
Ms Cooper said: "The problem is, that is just not people's experience at all.
"Instead people's experience is reporting a whole series of things and just getting no response at all, and including victims of serious abuse and hate crime, also reporting them and getting no response at all."
The hearing is taking place the day after Twitter suspended a number of accounts, including that of Britain First's deputy leader Jayda Fransen, who gained notoriety when three anti-Muslim videos she posted were retweeted by US president Donald Trump.
Other accounts which appear to have been suspended for violating the new rules are @BritainFirstHQ and that of leader Paul Golding, @Goldingbf.
Facebook's director of public policy, Simon Milner, and Dr Nicklas Berild Lundblad, Google's vice president for public policy in Emea, are also due to appear before MPs.