Comment by seabass-labrax

The primacy of European Union law applies to member states of the European Union. That is part of what the countries agreed to in order to become a member state. Some countries negotiated opt-outs for specific laws that they felt shouldn't apply to them before joining - and disgruntled member states could attempt the same by threatening to leave.

The only way that the European Union can 'force' compliance of a member state is for the EU Commission (or, exceptionally, the Parliament and Council) to withhold EU funds from that member state. Those funds were never the property of the member state in the first place though - again, no infringement on national sovereignty.