The National Organization for Marriage's (NOM) so-called Free Speech Bus was vandalized on Thursday in New York City.

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 USA Today, two people defaced the bus as it was parked near the United Nations for a scheduled event. Brown said that the vandals scratched the bus with a key, cracked windows with a hammer and spray painted slogans such as “Trans Liberation.”

“Boys are boys and girls are girls – it's very simple,” Brown told USA Today of the campaign's 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.”

Scheduled stops include New Haven, Boston, Philadelphia and Washington, DC.