Well there used to be the Socialist international... and the Greens have a fairly consistent general approach in most countries and are informally linked both directly and via like minded organisations such a Greenpeace.

I am not aware of an EU ban on transnational parties as such, although political parties do have to meet varying registration requirements in different countries to participate in elections and these can be quite stringent in some member states and not at all in others.

There are also obviously, close links between e.g. socialist, and also between Christian Democrat parties in various countries, and then you have the political groups within the EP which have got quite formal links and leadership structures.

Sinn Fein Ireland is also organised on an all-Ireland basis which of course straddles a sovereign border. So Libertas' claim to be pan-European is not all that unique, especially as it appears to be linking up opportunistically with all kinds of different groups in different countries and variously claiming to be Eurosceptic or pro-European depending on their alliances and where they think the floating votes are.

Global organisations such as the UN tend to be composed of Member States rather than citizens so the question of global political parties as such does not arise - although the member states do of course form regional and ideological alliances.

The notion of "human rights" is the first attempt to define individual rights within a global context - the primary actors in international law have always been states and trans-state organisations created by Treaties between states.  That notion could, of course, come to encompass a broader range of "citizen rights" within a global polity, but that doesn't seem to be on any agenda just yet.

The EU is however gradually moving beyond being an association of states to being a trans-state polity where EU citizens have voting, representation, legal, petition and consumer rights independently of their national polity and as such it could become a model for a broader Global polity in due course.

notes from no w here