WASHINGTON (Reuters) -U.S. Federal Trade Commission Chairman Andrew Ferguson alleged that Gmail uses what the FTC calls "partisan filtering" and raised the issue in a letter to the CEO of Google parent company Alphabet's, Sundar Pichai, the regulator said on Thursday.

"My understanding from recent reporting is that Gmail's spam filters routinely block messages from reaching consumers when those messages come from Republican senders but fail to block similar messages sent by Democrats," the letter released by the FTC claimed.

Google has denied similar claims from Republicans and conservatives in the past.