It must have been a slow news day when Halfords said they wanted suppliers to pay back money to their (large) customer to contribute towards a (very large) bill to revamp stores.
As I understand it, certain well known names (particularly in the retail industry) have been doing it for years. The difference here is that, on previous occasions, suppliers have been too afraid to mount any sort of legal challenge. Not this time. It would be interesting to see if the public shaming will be sufficient for Halfords to change its mind. Probably not (at least in the short term). Watch this space.
You can, however, bank on new clauses in long term supply contracts in the future which provide a legal framework to the practice (subject of course to UCTA).