Facebook has uncovered emails that appear to show Mark Zuckerberg’s connection to potentially damaging privacy practices at the company, the Wall Street Journal reported on Wednesday.

The emails were uncovered as part of a Federal Trade Commission (FTC) investigation that began after the Guardian reported that the personal data of 50 million Facebook users had been improperly harvested by Cambridge Analytica, a data firm that worked on Donald Trump’s election team and the winning Brexit campaign.

The unearthing of the emails has raised concerns inside Facebook that they would be harmful – at least from a public-relations standpoint – if they were to become public, the WSJ reported.

Facebook’s shares fell 2% on the news.

The Journal report said it could not be determined exactly what emails the FTC has requested and how many of them relate to Zuckerberg.

Facebook signed a consent decree with the FTC in 2012 after the regulator found it had “deceived” its customers by “telling them they could keep their information on Facebook private, and then repeatedly allowing it to be shared and made public”.

Under the 20-year settlement, Facebook was required to ask for permission before changing the way users’ personal information is released.

It has been working to settle the Cambridge Analytica scandal with the regulator and in April Facebook said it expected to pay $5bn to end the privacy investigation.

“Facebook and its executives, including Mark, at all times strive to comply with all applicable law, and at no point did Mark or any other Facebook employee knowingly violate the company’s obligations under the FTC consent order,” a company spokesman said in a statement.

“We have fully cooperated with the FTC’s investigation to date and provided tens of thousands of documents, emails and files.”

The FTC and the Department of Justice, which enforce antitrust laws in the United States, are gearing up to investigate whether Amazon, Apple, Facebook and Alphabet’s Google misuse their massive market power.