Anti-transgender activists are being met with protests as they drive through cities in the north-eastern United States in a big, orange bus emblazoned with the words "boys are boys" and "girls are girls."
The "Free Speech Bus" parked in front of the Massachusetts State House in Boston on Thursday morning, drew more than two dozen protesters holding signs and chanting, among other things, "No hate. No fear. Trans people are welcome here."
Democratic Mayor Marty Walsh, surrounded by dozens of supporters, raised a flag recognising the transgender community after the bus briefly stopped in front of City Hall.
Gregory Mertz, US director of CitizenGO, the Madrid, Spain-based group that's behind the bus tours, said organisers are pushing back against laws and policies accommodating transgender people.
"There's an agenda and movement that's saying it's OK for a boy to be a girl and that you can use whichever restroom you want," he said. "We think that's very harmful."
The bus's message is simply stating the "biological reality" that humans are "binary, sexually complementary creatures," said Joseph Grabowski, a spokesman for the National Organisation for Marriage.
The full text splashed across the bus's exterior reads: "It's Biology: Boys are boys . and always will be. Girls are girls . and always will be. You can't change sex. Respect for all."
Protesters said the message is overly simplistic.
"It assumes that our identities are the sum of what's between our legs," said Michelle Tat, a transgender woman from Boston.
The bus also stopped by Harvard University in nearby Cambridge on Thursday. It's slated to head south in the coming days, making stops in New Haven, Connecticut, Philadelphia and Baltimore before arriving in Washington DC, on April 3.
