Police in the US city of Pittsburgh are preparing for rioting should President Donald Trump fire special counsel Robert Mueller.
A memo from the police commander instructed detectives to bring riot gear to work “until further notice”.
The email said “there is a belief” that Mr Trump will soon fire Mr Mueller, prompting “large-scale” protests.
Mr Mueller is leading an investigation into alleged Russian meddling in the 2016 US presidential election.
But city officials say the decision was just a precaution and not due to any insight on Mr Trump’s plans.
“The protest would be semi-spontaneous and more than likely happen on short notice,” police commander Victor Joseph wrote in an email obtained by CBS News.
“Beginning Thursday, all major crimes detectives are required to bring a full uniform and any issued protective equipment (riot gear) with them to work until further notice.”
Mr Mueller’s investigation is also looking at whether there was collusion between Mr Trump’s campaign team and Russian agents to influence the 2016 election.
The president denies any wrong doing and has repeatedly expressed his frustration with the inquiry.
Pittsburgh Public Safety Director Wendell Hissrich said it was typical for the city to prepare for possible events or threats.
“In this case, we have not assessed the credibility of the potential for disturbances, and we do not have any knowledge of the president’s decision-making process.”
Democratic advocacy group MoveOn.org has organised a demonstration in Pittsburgh if Mr Mueller is fired, but according to CNN, it is unclear if the police memo was a result of the planned protest.
“We are getting ready in Pittsburgh to respond quickly and forcefully to a clear obstruction of justice,” the group’s online event page says, adding that emergency protests are planned in major cities across the US.
More than 2,300 people have registered to participate in the protest so far, according to the Pittsbrugh Post-Gazette.
Pittsburgh Mayor Bill Peduto confirmed that the memo had been sent to the city’s detectives.