 Both countries joining the NATO (Poland in 1999, Lithuania in 2004, with Poland being a vocal supporter of Lithuania's accession) and European Union (both in 2004).However, in the late 2000s, disagreements over Lithuania's implementation of the Friendship Treaty have soured relations and cooperation on energy issues.The electricity grids of Poland and Lithuania are inter-connected but the gas pipelines of the two countries are only connected through a Russian-controlled gas pipeline.