The U.S. Office of Special Counsel has reportedly opened a case file into whether the photo Interior Secretary Ryan Zinke Ryan Keith ZinkeTrump extends Florida offshore drilling pause, expands it to Georgia, South Carolina Conspicuous by their absence from the Republican Convention Trump flails as audience dwindles and ratings plummet MORE tweeted of him wearing "Make America Great Again" socks violated federal ethics laws.

CNN on Tuesday reported that the internal federal watchdog opened the case after receiving a complaint from the liberal watchdog group Campaign for Accountability.

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The CNN report notes that the Office of Special Counsel is assessing if Zinke violated the Hatch Act, which prohibits political activity by government officials on the job.

“I can confirm that OSC received the complaint and has opened a case file. However, I'm unable to comment on or confirm whether an investigation has been opened,” Office of Special Counsel spokesman Zachary Kurz told CNN.

The controversy stems from a photo Zinke tweeted of him wearing socks featuring President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE's campaign slogan.

“Breaking in new socks on a hike with the governors today,” the official @SecretaryZinke Twitter account said in a June tweet.

Zinke later deleted the tweet and posted an apology on Twitter, saying that he did not realize it “could be viewed as a political slogan. I’ve deleted it and apologize for the mistake.”

"I remain excited about all the incredible policy work POTUS is doing,” the tweet added, with the campaign slogan blacked out in the photo.

.@SecretaryZinke deleted this tweet, a clear violation of the Hatch Act. pic.twitter.com/qILMnXSDOg — Accountability (@Accountable_Org) June 26, 2018

Executive Director of the Campaign for Accountability Daniel Stevens said in a statement last month that Zinke “continues to play fast and loose with federal ethics laws.”

According to the Special Counsel's updated guidance released on March 5 about the Hatch Act, it says that “while on duty or in the workplace, employees may not: wear, display, or distribute items with the slogan 'Make America Great Again' or any other materials from President Trump’s 2016 or 2020 campaigns.”