Poland are to temporarily suspend Schengen and reintroduce border controls between 4th July – 2nd August, in connection with the NATO Summit, taking place in Warsaw, (8th-9th July) and World Youth Day, due to be held in Kraków (25th-31st July).
Under the terms of the Schengen Agreement, countries are permitted to reintroduce border checks in certain circumstances, which many countries have over the years for specific events, football tournaments, G8 etc and in response to heightened security threats.
Poland has previously suspended Schengen during the Warsaw Climate Change protests and Euro 2012 championships.