The National Organization for Marriage's (NOM) so-called Free Speech Bus was chased out of Philadelphia on Saturday.

The orange bus' message reads: “It's Biology: Boys are boys … and always will be. Girls are girls … and always will be. You can't change sex. Respect all.”

The bus is sponsored by NOM, the International Organization for the Family (IOF), whose formation was announced by NOM President Brian Brown in December, and a coalition of global groups opposed to LGBT rights.

According to The Philadelphia Inquirer, about 100 people gathered outside City Hall for a Pop-Up Love Party organized by the city's Office of LGBT Affairs and other groups.

Organizers said that they were there to support the transgender community and were unaware of when the bus would arrive in Philadelphia.

The bus arrived moments after the speakers finished.

The bus was hit with eggs and at least two smoke bombs were set off. Protesters chanting “Trans lives matter” blocked the bus from moving forward. Police arrested at least one person.

A police captain boarded the bus. “I asked [the driver] if his intention was to leave. He said it was,” the captain said.

The incident lasted about 15 minutes, the paper reported.

In a previous interview with USA Today, NOM President Brian Brown explained the bus' message.

“We don't want men in girl's restrooms. We don't want schools and our law attempting to say that people are bigoted simply because they understand that there's a difference between male and female,” Brown said.