The Federal Communications Commission is facing bipartisan pressure to investigate how potentially millions of bogus comments were filed for and against the agency’s repeal of neutrality protections.

Sen. Jeff Merkley, Oregon Democrat, and Sen. Pat Toomey, Pennsylvania Republican, wrote FCC Chairman Ajit Pai on Monday seeking answers about the onslaught of fake comments filed on the agency’s website last year as commissioners weighed rescinding the Obama-era internet regulations.

The identities of as many as two million Americans were stolen and used to file fake comments during the FCC’s comment period, including those of both Mr. Merkley and Mr. Toomley, the lawmakers wrote in their letter to Mr. Pai.