WASHINGTON (Reuters) - Interior Secretary Ryan Zinke on Tuesday deleted a photo of a sock he was wearing with President Donald Trump’s “Make America Great Again” campaign slogan on it after realizing he may have violated a law that prohibits federal employees from engaging in political activity.

FILE PHOTO: U.S. Secretary of the Interior Ryan Zinke testifies in front of the Senate Committee on Energy and Natural Resources on Capitol Hill in Washington, U.S., March 13, 2018. REUTERS/Eric Thayer/File Photo

While attending a meeting of the Western Governors Association at South Dakota’s Mount Rushmore, Zinke tweeted a photo of his leg covered with a sock with Trump’s image on it and his Make America Great Again campaign slogan.

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

Several tweeters and watchdog groups were quick to observe that donning campaign-style apparel while conducting official business is a violation of the Hatch Act.

The Campaign for Accountability responded to the @SecretaryZinke tweet with a link to a March 5 letter posted by the Office of Special Counsel (OSC), which updated its guidance on the Hatch Act in light of Trump confirming he will run for re-election.

“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; use hashtags such as #MAGA or #ResistTrump in social media posts or other forums; or display non-official pictures of President Trump,” the letter said.

Later in the afternoon, Zinke replaced his earlier tweet on his official account with a photo of the same sock with “Make America Great Again” blacked out.

“Earlier I tweeted a pic of my new socks not realizing it had what 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 said.

Watchdog groups and Democratic lawmakers have been eying Zinke’s official and political activities.

Earlier this month, the Office of Special Counsel cleared Zinke of allegations of improper political activity under the Hatch Act when he spoke to the Las Vegas Golden Knights, a professional hockey team owned by one of his campaign donors, in June 2017.

In March, two Democratic lawmakers asked for an OSC investigation into whether Zinke violated the Hatch Act when he traveled to Pennsylvania to announce funding for a coal mine reclamation site in February. Several local Republican politicians attended, including Rick Saccone, who ran in a high-profile special election in the neighboring district just days later.

The Interior Dept. was not immediately available for comment.