Big tech is coming under renewed political pressure following the mass shootings at two New Zealand mosques on Friday.

The attack was livestreamed on Facebook before spreading like wildfire online, leaving tech companies scrambling to block the footage.

The CEOs of Facebook, YouTube, Twitter, and Microsoft have been asked to attend a homeland security briefing.

Three major New Zealand telecoms companies have also weighed in, asking that the CEOs of Facebook, Twitter, and Google take part in urgent talks about "harmful content."

Facebook, Google, Twitter, and Microsoft are all coming under mounting political pressure to answer questions following the mass shootings at two mosques in Christchurch, New Zealand on Friday.

The attack was livestreamed on Facebook before spreading like wildfire online, leaving tech companies scrambling to block the footage.

Facebook announced on Sunday that it removed 1.5 million uploads. YouTube did not disclose the exact number of videos it removed, but said it was in the tens of thousands.

Read more: YouTube's human moderators couldn't stem the deluge of Christchurch massacre videos, so YouTube benched them

Rep. Bennie G. Thompson, the chairman for the US Committee on Homeland Security, sent a letter on Monday to the CEOs of Facebook, YouTube, Twitter, and Microsoft, requesting a briefing on March 27.

"This video was widely available on your platforms well after the attack, despite calls from New Zealand authorities to take these videos down," Rep. Thompson wrote, adding that violent acts of terrorism going viral could inspire "copycats."

Rep. Bennie G. Thompson, chairman of the US Committee on Homeland Security. Reuters

"You must do better. It is clear from the recent pattern of horrific mass violence and thwarted attempts at mass violence — here and abroad — that this is not merely an American issue but a global one," he wrote.

Thompson also threatened that if tech companies don't take the necessary steps to prevent the proliferation of violent ideologies on their platforms, Congress will have to step in.

Tech companies aren't just coming under pressure from politicians. In New Zealand, three major telecom companies and internet providers sent an open letter on Tuesday to Facebook CEO Mark Zuckerberg, Twitter CEO Jack Dorsey, and Google CEO Sudar Pichai, asking that they attend an "urgent discussion" on harmful content.

"We appreciate this is a global issue, however the discussion must start somewhere. We must find the right balance between internet freedom and the need to protect New Zealanders, especially the young and vulnerable, from harmful content," said the bosses of Vodafone NZ, Spark and 2degrees.