Federal Trade Commission (FTC) Chairman Andrew N. Ferguson warned Gmail, the world’s largest email service, this week that it may face a federal investigation over allegations that the company intentionally suppresses messages sent by Republicans.

“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,” Ferguson wrote in a letter Thursday to Sundar Pichai, the CEO of Google parent company Alphabet.

Ferguson cautioned in the letter that inconsistencies in Gmail’s spam filtering based on politics “could lead to an FTC investigation and potential enforcement action.”

“A consumer’s right to hear from candidates or parties, including solicitations for donations, is not diminished because that consumer’s political preferences may run counter to your company’s or your employees’ political preferences,” the Trump-appointed FTC chair wrote.

“If Gmail’s filters keep Americans from receiving speech they expect, or donating as they see fit, the filters may harm American consumers and may violate the FTC Act’s prohibition of unfair or deceptive trade practices.”

Republicans have long complained that Gmail’s spam filters divert GOP emails away from users’ inboxes at a high rate. The company has repeatedly denied improperly applying filters.

“Gmail’s spam filters look at a variety of objective signals – like whether people mark a particular email as spam, or if a particular ad agency is sending a high volume of emails that are often marked by people as spam,” a Google spokesperson said in a statement to The Hill on Friday. “This applies equally to all senders, regardless of political ideology.”

“We will review this letter and look forward to engaging constructively,” the company added.

A federal judge dismissed a lawsuit in 2023 that the Republican National Committee (RNC) filed against Google, accusing the company of trying to “secretly suppress the political speech and income of one major political party” by marking Republican emails as spam.

U.S. District Judge Daniel J. Calabretta wrote in that ruling that other factors could be contributing to the filtering of RNC emails, noting “the RNC sends out a significant number of emails to individuals on its list.”

“While it may be that some, perhaps many, users specifically wanted each and every one of those emails, Google could reasonably consider these emails as mass mailings to be objectionable, just as it can for other email senders,” Calabretta wrote. “In this case, the RNC’s allegation that Google acted in ‘bad faith’ does not rise above the speculative level.”

The Federal Election Commission (FEC) also dismissed a complaint from the RNC about Gmail that year which alleged the company had effectively made “illegal corporate in-kind contributions” to Democrats by filtering Republican emails to spam folders.

“Google has credibly supported its claim that its spam filter is in place for commercial reasons and thus did not constitute a contribution,” the FEC wrote.