‘May I just add, Mr Lipwig, that behind you there is a door. If at any time in this interview you feel you wish to leave, you have only to step through it and you will never hear from me again.’

Moist filed that under ‘deeply suspicious’.

[…]

Moist looked at him. ‘Excuse me,’ he said, standing up, ‘I’d just like to check something.’

There were two men dressed in black standing behind his chair. It wasn’t a particularly neat black, more the black worn by people who just don’t want little marks to show. They looked like clerks, until you met their eyes. They stood aside as Moist walked towards the door which, as promised, was indeed there. He opened it very carefully. There was nothing beyond, and that included a floor. In the manner of one who is going to try all possibilities, he took the remnant of spoon out of his pocket and let it drop. It was quite a long time before he heard the jingle.

Then he went back and sat in the chair.

‘The prospect of freedom?’ he said.

‘Exactly,’ said Lord Vetinari. ‘There is always a choice.’

‘You mean . . . I could choose certain death?’

‘A choice, nevertheless,’ said Vetinari.

Terry Pratchett, Going Postal

Technically speaking it is illegal for prisoners to be coerced into labor in the US - but it’s often strongly encouraged.

Either fight fires or fight inmates