Starbucks, Apple, Amazon, McDonald's...do you notice a pattern? The suggestion that the Commission is not targeting big US companies is comical (especially in the light of similar actions with other justifications, like the 2.7b fine on Google for their shopping search), as is their interpretation of both tax law and illegal state aid.
The commission doesn't even challenge the transfer pricing laws, they just interpret them differently and based on their interpretation they decide that the tax authorities have granted a selective advantage. The procedure is completely arbitrary as its entire basis is the disagreement between the commission and the tax authorities. Given the complexity of corporate structures and tax law, and the inherent ambiguities of things like transfer pricing, such disagreements can be generated wherever the commission wants to find them. If they wanted to target Chinese companies it would be trivial to conjure up similar issues.
It's particularly ironic that a law against selective treatment of corporations is being used to selectively punish some of them.