Jair Bolsonaro – likened to US President Donald Trump – has often refused to comply to the regulations despite the country’s deepening health and political crisis.
Brazil has more confirmed coronavirus cases and deaths than anywhere outside of the United States.
More than 1.1 million have been infected with over 51,000 known to have died from Covid-19.
The unrest has prompted numerous demonstrations in recent weeks and many blame the leader for the high death figures.
President Bolsonaro’s decision to oppose lockdowns and focus on the country’s economy has been hugely divisive throughout the country.
A judge has now warned that he faces a big fine if he refuses to comply and continued to disobey a local ordinance in the federal district meant to slow the pandemic.
Federal Judge Renato Borelli ruled in a decision made public on Tuesday that he was subject to a fine of 2,000 reais – around £310 – for every day he ignores the demands.
The right-wing populist caused outrage when he attended political rallies without one in the middle of the world’s second-worst coronavirus outbreak.
Brazil’s solicitor general, which argues the government’s legal interests, said in a statement that it was studying ways to reverse the decision.
The toll has made the country a prime location for vaccine trials, which began over the weekend for a candidate developed by Oxford University.
Brazil’s interim health minister said on Tuesday that the government would likely sign a deal this week to produce the university’s trial vaccine locally.
On other fronts, Bolsonaro has openly defied the consensus among public health experts for slowing the outbreak.
The president has criticized lockdown and social-distancing orders issued by governors and mayors, saying their economic damage is worse than the disease.
Echoing Trump, Bolsonaro has also pushed unproven anti-malarial drugs to treat the novel coronavirus.
But his most visible defiance has been going mask-less at a string of demonstrations in Brasilia.
He was pictured holding babies for photos and shaking hands with supporters.
Other officials have fallen foul of the local mask rule.
The country’s former education minister, who resigned last week, was fined 2,000 reais for not wearing a mask on the capital’s central boulevard earlier this month.