A nurse's car was clamped for five hours when she used a patient's private parking space in Essex.
Hannah Bannock was in uniform and had displayed an NHS permit when she was clamped in Clacton on Monday, the North East Essex Primary Care Trust said.
Spokesman Peter Richardson said it "beggared belief" that Mrs Bannock was forced to postpone visits.
The government is expected to confirm later that clampers are to be banned from private land in England and Wales.
'Totally above law'
Mr Richardson said the nurse was initially fined "somewhere in the region of £850" but it was understood the trust had been told it would not have to pay for the fine.
"One of our nurses has been hamstrung for the whole day and these people seem totally above the law," he added.
Mrs Bannock told BBC Essex she refused to get out of the car to prevent it being towed away and the clamp was eventually released at 1645 BST.
A spokesman for South East Clamping was unavailable for comment.
Mrs Bannock said she had parked her car to visit patient Iris Griffin for 15 minutes.
"They had only just put the clamp on. I raced up to him [the wheelclamper] and told him to take it off, that I was a district nurse and that I had seven or eight patients left to see.
"He said 'sorry, not my problem, phone the number and then it can be released'."
'Refused to move'
She said she called a number on a sticker attached to her windscreen and was told it would cost £350 to release her car, and £50 for each further half hour.
Two managers from the primary care trust arrived to support her and the three of them "sat it out" with the wheelclampers for more than five hours, she added.
"After two hours, they said if I was unwilling to pay they would tow it away and take it to a compound and then they would have charged even more," she said.
"Thankfully I sat in my car and basically refused to move."
She said she understood that she should have used a residents' permit, but her patient did not have one, and she had not encountered problems before.