Taoiseach Leo Varadkar is in Brussels this morning for an EU Council meeting.
Leaders of the EU27 are expected to discuss proposals for changes to the composition of the European Parliament, post-Brexit.
The UK currently has 73 MEPs - almost 10% of the total amount of seats.
It is currently proposed that the size of the parliament will shrink from 751 to 705 MEPs once the UK leaves - with some of the UK's seats redistributed, and others placed in 'reserve' in case any other countries join the EU in the future.
The long-term budget of the union after the UK leaves will also be discussed at today's 'informal summit'.
The new budget will cover the years after 2020.
In an invitational letter to EU leaders, European Council President Donald Tusk said: "In October last year, we agreed to conduct a debate about our priorities, so that the European Commission can receive political guidance from the European Council, before coming up with its proposals. In recent debates we have set out new priorities, such as stemming illegal migration, improving European security and defence as well as investing more in the Erasmus programme.
"Additionally, we will have to face the issue of a gap in the EU budget due to Brexit. This shows the seriousness of the challenges ahead."
Theresa May will not be in attendance at the summit.
The British Prime Minister spent yesterday in a lengthy 'war cabinet' meeting as senior ministers attempted to reach an agreement on plans for the UK’s future relationship with Europe.
Mrs May is set to outline her plans in a speech next week.