The choice of attire is a pressure tactic related to an ongoing battle with the provincial government over their collective agreement.
The 80 Montreal courthouse constables who provide security in the building donned jeans and camouflage-style pants, much to the chagrin of the magistrates.
A union representative said constables assigned to courtrooms were told to wear jeans, but the judges ordered them to change, invoking decorum.
Activities were back to normal after about 20 minutes when constables assigned to courtrooms complied and changed back to their usual uniforms.
But their colleagues monitoring the courthouse corridors remained in camouflage pants.
Union spokesman Jacques Daoust said it isn't the first time the constables have engaged in such tactics and judges have tolerated it in the past.
That may be changing: on Wednesday, judges in Gatineau told guards to remove union-issue armbands with slogans they'd started wearing this week.
Daoust says the constables were simply expressing their frustration the only way they can.
The constables are provincial government employees.
Thursday's controversy comes on the heels of one involving Montreal police officers who were criticized for wearing camouflage pants to former premier Jacques Parizeau's funeral this week.
The police officers have been wearing camouflage pants and red baseball caps since last year, protesting against the province's pension reforms.
It prompted condemnation from Montreal's mayor and Quebec Premier Philippe Couillard.
Couillard said the provincial government intends to introduce measures this fall to ensure peace officers wear their uniforms.
In Quebec City, Justice Minister Stephanie Vallee said peace officers should always be in uniform.
"It's a question of respecting what they represent and they enforce the law," Vallee told reporters Thursday. "They should dress properly."
Note to readers: This is a corrected story. An earlier version said the courthouse constables were protesting pension reforms.