His government introduced tougher limits on immigration and a freeze on tax rates ("skattestoppet" in Danish). Certain taxes were lowered, but his coalition partners in the Conservative People's Party repeatedly argued for more tax cuts and a flat tax rate at no higher than 50%. Rasmussen's government implemented an administrative reform reducing the number of municipalities ("kommuner") and replacing the thirteen counties ("amter") with five regions which he referred to as "the biggest reform in thirty years". He authored several books about taxation and government structure. He resigned as Prime Minister in April 2009 to become Secretary General of NATO. His term as Secretary General was to end in the summer of 2014, but the North Atlantic Council extended his term on 11 December 2013 until 30 September 2014 in order to ensure the organisation of the 2014 NATO summit in Newport, United Kingdom. He is a member of the Honorary Board at the Bussola Institute and a Senior Network Member at the European Leadership Network (ELN).