WASHINGTON, DC (NEXSTAR) — Senate Republicans continued their attack on Big Tech Thursday, this time accusing social media companies of censoring the origins of COVID-19.

A group of GOP lawmakers blames the tech platforms for limiting discussion of the now growing theory that the virus leaked accidentally from a Chinese lab.

“They have stepped over the line on this one,” said Sen. Marsha Blackburn, R-TN.

“This is a serious, grave threat to freedom and the open exchange of ideas under our Constitution,” said Sen. Roger Wicker, R-MS. “Twitter moved to censor any coronavirus coverage that they thought in their judgement might cause widespread panic. How does a multi-rich, powerful internet platform get to make that decision? I could go on and on and on.”

Wicker introduced legislation Thursday to stop companies from controlling online speech, including prohibiting platforms from taking action against users based on ethnic, partisan, racial, religious or sexual grounds.

“These large internet tech platforms cannot discriminate based on their own opinions and based on what they think the public should and should not be allowed to hear,” he said.

The European Union just joined the United States’ call for a new World Health Organization investigation into the origins of the pandemic while President Joe Biden continues to meet with world leaders.

“We all want to get to the bottom of what happened here,” White House Press Secretary Jen Psaki said during a briefing on the topic last week.

Last month, the White House ordered American agencies to conduct a 90-day review of the origins, but Blackburn argues Senate committees should take the lead.

“It is our job to get to the bottom of what happened,” she said.

Blackburn also wants to make it easier for Americans to sue China over the pandemic and give federal agencies, specifically the CDC and FDA, a stronger presence in the country.

Virus researchers have not publicly identified any new evidence to strengthen the lab-leak hypothesis. They have said though it is unlikely that a definitive answer about COVID-19’s origins would soon be available. That work usually takes years or decades.