brussels european commission head jean-claude juncker invite leaders four eastern european countries dinner accord letter see reuters effort ease tensions wealthy western member state letter date oct. address leaders poland hungary czech republic slovakia juncker stress paramount importance eu unity strain dispute immigration issue well brexit prague bratislava sometimes strike moderate tone warsaw budapest constantly loggerheads bloc executive commission brussels well eu heavyweights germany france bloc increasingly see flout democratic rule juncker propose dinner leaders four visegrad group nations brussels oct. 18 ahead eu summit oct. 19-20 cite need build unite strong democratic europe despite britain exit believe preserve unity remain 27 process paramount importance say eastern state especially poland hungary resist eu program member state accept refugees mass influx people 2015-16 mostly muslims middle east africa point contention include reform eu labor rule france western state say give unfair competitive advantage cheap workers east western countries notably italy frontline take refugees migrants across mediterranean suggest cut generous aid provide easterners eu budget fail show european solidarity migration slovak prime minister robert fico recent reassurances country member single-currency euro zone see firmly heart eu seem go well brussels commission respond say would work slovakia eastern member state tackle see malpractice second-class food products sell big western multinationals home market soothe relations poland hungary however prove challenge poland lead eurosceptic law justice party pis unprecedented eu investigation rule law follow series reform critics say threaten independence polish judiciary eu also face tough challenge agree next multi-year budget run 2021 generous handouts eastern nations particular threat britain lead net donor prepare leave bloc 2019. pro-eu centrist emmanuel macron french presidency year brussels hop reinvigorate paris-berlin alliance help usher reform need bloc thrive despite brexit franco-german axis promise strong years easterners either play along lose senior eu diplomat say eu 's juncker court eurosceptic easterners dinner invite