Two federal lawmakers are raising concerns about whether new 5G technologies will cause cancer.

Specifically, Sen. Richard Blumenthal, D-Conn., and Rep. Anna Eshoo, D-Calif., sent a letter (PDF) to FCC Commissioner Brendan Carr asking for guidance on the topic.

“To ensure we communicate accurate information to our constituents … we respectfully request you provide to our offices the 5G safety determination from FCC and relevant health agencies,” they wrote. “Most of our current regulations regarding radiofrequency safety were adopted in 1996 and have not yet been updated.”

They added that the FCC's specific absorption rate (SAR) limits do not apply to devices operating above 6 GHz and pointed out that some 5G communications occur at 24 GHz or above.

“Furthermore, the final results of the world's largest and most expensive study to date on the link between radiofrequency radiation and cancer were only just released on November 1, 2018 by the National Toxicology Program (NTP),” the legislators wrote. “As you know, this study found evidence of cancerous heart tumors, as well as some evidence of cancerous brain tumors, in male rats exposed to exposed to high levels of radiofrequency radiation like that used in 2G and 3G cell phones. However. researchers have cautioned that findings ‘do not apply to 4G or 5G technologies.’”

A representative from Commissioner Carr’s office did not immediately respond to questions about the letter.