The question is quite straightforward, as in the title.
I found myself discussing with a colleague the fact that according to some, fines should not be an absolute amount (e.g. 50 USD/EUR) but rather a percentage of the monthly income of the fined person (e.g. 1%).
The rationale brought forward is that such a system would be neutral, while the current one favours high income people, as they, feeling less affected by fines, are less inhibited by them.
Is there a proper political theory discussing the benefits and drawbacks of such an idea? Possibly also taking into account socio-economic considerations.