A temporary fence will once again be erected around the Capitol building for a pro-Trump demonstration on Sept. 18.

Donald Trump supporters have organized a “Justice for J6” rally to seek justice for hundreds of protesters who they claim to have been unfairly injured, imprisoned or convicted due to the Capitol riots on Jan. 6.

U.S. Capitol Police is already monitoring “concerning” online conversations about the planned event, and will crack down on misbehaving demonstrators.

“We are here to protect everyone’s First Amendment right to peacefully protest,” Capitol Police Chief Tom Manger said in a statement. “I urge anyone who is thinking about causing trouble to stay home–we will enforce the law and not tolerate violence.”

The Capitol Police Board has issued an emergency declaration, allowing the department to deputize external law enforcement officers as Capitol Police special officers.

CBS News cited intelligence that estimates between 300 to 500 people will attend the “Justice for J6” rally. Some Congress members have also been invited to attend.

Fox News revealed the rally will be held at the Union Square plaza, on the Capitol’s west lawn. Look Ahead America will organize the event, led by Matt Braynard–a former Trump campaign employee.