The specific grounds for the fine by the Fair Trade Commission are not made clear in the brief article however, if as is stated in the article the Taiwanese com

The specific grounds for the fine by the Fair Trade Commission are not made clear in the brief article however, if as is stated in the article the Taiwanese companies had obtained reseller rights to set a price and then this was being undermined by Apple then this is not particularly fair of Apple to then attempt to set those resale prices. I use the word 'fair' deliberately in reference to the Fair Trade Commission. At the same time, it is likely to be anti-competitive to allow an upstream manufacturer to fix prices with all retailers on the basis that customers are prejudiced and retailers are unable to compete on price. This is the main answer to your question. Also if only one retailer plays ball with Apple then they have a monopoly position again to the likely detriment of customers. The arrangement is however acceptable where the retailer plays the role of mere agent in the arrangement (i.e. takes minimal risk in the transaction as compared to a distributor) as here it is reasonable for the manufacturer to set downstream prices. However here if the article is correct, then the presence of a clear right for the distributor to set prices which is then subsequently ignored by Apple would seem to justify action by Taiwanese FTC. If anything this would be a breach of contract issue also providing another ground for the FTC to intervene. Perhaps in this case, Apple intended to make the contract transparent by granting the right to the retailer to determine resale prices (in compliance with local law potentially) but then behind the scenes exerted pressure. This is pure speculation of course.