A disabled woman and her mother returned from a shopping trip to find a threatening note on their car about "illegal use of a blue badge space" despite them owning a valid permit.
Julie Tanner and her daughter Paige were in Reading when they found the hand-written message claiming neither had any visible "sign of disability".
Paige, 23, is severely mentally disabled and needs one-to-one support.
The family said the person "should not judge" unaware of the full details.
Mrs Tanner, a mother-of-four, told the BBC she and her daughter had been shopping at the Woodley Precinct, Woodley, on Monday before they returned to find the angry scribbled note.
It said: "You will be reported for illegal use of a blue badge space.
"I witnessed you and your young able-bodied daughter park the car at 13:10 on 19 February 2018 and walk towards the precinct with no sign of disability.
"This selfish action deprives a disable person of somewhere to park."
Paige attends a day care centre three-and-a-half days a week and suffers from behavioural and anxiety issues.
Her father Alan posted a picture of the note on Facebook, and said he hoped the person who wrote the message saw his post.
Comments on the post said the note was "disgusting" and "unbelievable" and urged people to "think before they judge".
One said: "The old saying 'you should never judge a book by its cover' comes to mind. People that don't know you don't know the situation and have no right to judge you or your family."
Mrs Tanner said she called the council to confirm the family had a legitimate badge in case a report was made.
She added: "We have to do it for our own daughter, so she can get the best out of life."