Explainer-Why are the EU and UK arguing over Northern Ireland?

FILE PHOTO: A 'No Hard Border' poster is seen below a road sign on the Irish side of the border between Ireland and Northern Ireland near Bridgend, Ireland October 16, 2019. REUTERS/Phil Noble

(Reuters) - British Brexit minister David Frost called in a speech in Lisbon on Tuesday for the European Union to allow "significant change" to post-Brexit rules governing trade with Northern Ireland.

He was speaking a day before the EU presents its proposals to solve a standoff over part of the Brexit divorce deal.