Nothing is decided at EU level unless all member countries have explicitly agreed by treaty to do so, and even then each piece of legislation is agreed by national governments. For sensitive matters like tax and foreign affairs, the requirement for this agreement is complete unanimity, and in other areas there is a very high "qualified majority" threshold. (A "qualified majority" is defined as: 55% of member states, representing at least 65% of the EU population)
This means that no one state (or minority of states) can impose a measure on other member states, and that smaller states cannot override states with larger populations.
