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 Sundar Pichai, the CEO of Google parent company Alphabet, 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 said.

A Google spokesperson said Gmail's spam filters apply equally to all, regardless of political ideology.

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

Republicans have long accused big tech companies of discriminating against and suppressing conservative views, an assertion the companies deny. Many tech firms have in recent months aimed at building warm ties with Republican President Donald Trump, who took office in January.

The Google spokesperson said the company will review the letter and engage "constructively" on it.

"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. This applies equally to all senders, regardless of political ideology," the spokesperson added.

The FTC chair's letter warned the company that not being consistent with FTC regulations "could lead to an FTC investigation and potential enforcement action."

A U.S. judge has previously dismissed the Republican National Committee's lawsuit accusing Google of intentionally misdirecting the political party's email messages to users' spam folders.