Madrid authorities have impounded an orange-and-white bus used by a group campaigning against teaching schoolchildren about transgender people.
Police stopped the bus from returning to the Spanish capital's streets to prevent a hate crime, Madrid mayor Manuela Carmena said.
The eye-catching bus has several anti-transgender phrases written on its sides.
One says: "If you're born a man, you're a man. If you're a woman, you will always be a woman."
The vehicle created an outcry after it first appeared in public on Monday.
The bus belongs to the Hazte Oir (Make Yourself Heard) organisation, which has previously opposed abortion rights.
The group opposes a campaign in Spanish schools last month by an association of families with transgender children that aimed to raise awareness of the issue.
The Hazte Oir organisation said in a statement that it disapproved of teaching "sexual diversity", which it criticised as introducing the "dogma of the homosexual lobby in schools".
Gender identity is unrelated to sexual orientation, according to most experts.