Around 30 banner-waving protesters dressed as various superheroes stopped at the courts during a street demonstration through Bristol in support of fathers' rights.
Around 10 protesters dressed as Spiderman, Batman, Superman and The Incredibles forced their way into the court and chanted "What do we want? Justice. When do we want it? Now."
A fire alarm was activated, although court staff could not confirm who was responsible, and nearly 100 staff flooded into the street outside.
Two police vans arrived, along with two fire engines, and the men soon left the court building and continued their march.
The demonstration was joined by two campaigners who scaled the roof of deputy Labour leader Harriet Harman's home in Herne Hill, south London, earlier this week.
Jolly Stanesby and Mark Harris, both from south Devon, started the rooftop protest on Sunday and continued for more than 24 hours. They have since been bailed by police.
Mr Stanesby, from Ivybridge, said: "We always have a little get-together before Father's Day to put our message across."
Fathers 4 Justice is a civil rights group which campaigns for parental equality and a father's right to see his children.
Mr Stanesby added: "Just because my ex decided to move on to another boyfriend shouldn't mean I don't get to see my child.
"Her new boyfriend can see my child as long as he likes, whereas I have to apply and have boundaries. I have to have checks, doctor reports... The courts are corrupt."
Mr Stanesby said he and Mr Harris have written to Ms Harman to request a meeting with her.
He said: "She's Minister for Justice and Minister for Women - how can those two things go together?"
Mr Harris, from Plymouth, said opening family courts to the public was one of the focal points of the Fathers 4 Justice campaign.
He said: "Open up the courts so people can see the ridiculous decision made against fathers. I was once sent to prison for waving at my daughters."
The march started at The Pithay and moved up to Perry Road via Corn Street and Colston Avenue, where the group unveiled a new poster campaign.
The poster showed an image of a child dressed in a superhero costume and read: "If this little superhero doesn't see his daddy on Father's Day, he doesn't see half his family."
