I reflect on which sanctions might be taken by the EU against Russia since they demonstrate again by the case of Navalny how they treat human rights of the oppostion in Russia. Since my research on the internet didn't deliver me a hint on which laws are relevant to be considered in the case of possible sanctions, I wanted to ask you for a hint.
Here is an overview about the process the EU uses for sanctions.
But keep in mind that sovereign states are not required to allow trade with each other (unless they signed treaties to that effect, and in theory they could withdraw from treaties). So it comes down to the political will of the EU, and the EU is the union of sovereign states. Some are more critical of Russia, others less so. They have left themselves enough latitude to allow a political decision if they want to further confront Russia, or not.
So laws are not really relevant here. The EU decides if it fights for principle or if political expediency wins out.