The House Homeland Security Committee chairman called on tech leaders Tuesday to explain how a violent video of Friday's New Zealand mosque shooting spread on their platforms.

Rep. Bennie Thompson, a Democrat from Mississippi, wrote to the CEOs of Facebook, Twitter, Microsoft and Google's YouTube to request a briefing in front of the committee on March 27. Thompson asked the leaders to explain how they handled the video's spread, which appeared to depict one of two mosque shootings in Christchurch, New Zealand, on Friday that killed at least 50 people.

Following the attacks, YouTube, Facebook, Twitter and others scrambled to remove copied versions of the alleged shooter's video that kept popping up on their platforms. Some users were able to override automatic screens by altering the video, forcing YouTube to take unprecedented steps to reduce the video's spread, including suspending the ability to filter results by upload date. In the 24 hours after the suspect livestreamed the attack on Facebook, the company said it removed 1.5 million videos of the event, 1.2 million of which were blocked before they were even live on the site. But even so, the company later shared that the video of the attack was viewed over 4,000 times before it was removed.

Facebook, YouTube, Twitter and Microsoft formed the Global Internet Forum to Counter Terrorism (GIFCT) in 2017 to invest in solutions to reduce the spread of online terrorist content. While Microsoft was not implicated in the spread of the New Zealand mosque shooting video, Thompson seems to have called on its leader because of its role in GIFCT.

Thompson called out what he perceived as a disparity between how the tech companies have handled the removal of terrorist content related to ISIS and Al-Qaeda compared to that of "other violent extremists, including far-right violent extremists." The congressman points to a stat on the GIFCT website that says, "99% of ISIS and Al Qaeda-related terror content that is removed from Facebook is content that is detected before anyone in its community has flagged it." He argues the public should be granted the same transparency around content distributed by other violent extremists.

"Studies have shown that mass killings inspire copycats — and you must do everything within your power to ensure that the notoriety garnered by a viral video on your platforms does not inspire the next act of violence," Thompson wrote.

A Facebook spokesperson confirmed the company "will brief the committee soon." Microsoft, YouTube and Twitter did not immediately return CNBC's requests for comment on the letter.

"Your companies must prioritize responding to these toxic and violent ideologies with resources and attention," Thompson wrote. "If you are unwilling to do so, Congress must consider policies to ensure that terrorist content is not distributed on your platforms—including by studying the examples being set by other countries."

Here's Thompson's full letter: