Serbian Prime Minister Aleksandar Vucic sent a protest letter to EU officials on Wednesday, saying "with aggressive and unacceptable measures, Croatia has drastically struck our national and vital economic interests as well as strongly undermining regional relations and stability." Hungary's prime minister says wants the whole world to share the burden of housing refugees and migrants. Orban also repeated a suggestion for EU countries to help Greece protect its borders to prevent migrants flowing into the continent, saying member states could volunteer troops for such a mission. According to a government document obtained by The Associated Press and interviews with officials and migrants, the moves so far appear to be ad hoc and aimed only at preventing migrants from reaching the Turkish frontier city of Edirne, where hundreds are staging a sit-in near the Greek border. Ahmet Icduygu, who directs the Migration Research Center at Istanbul's Koc University, says it's a sign of a more determined effort by Turkey to get a handle on the country's massive refugee population. The European Union's executive arm is opening 40 new infringement cases against 19 member states for failing to implement the 28-nation bloc's common asylum rules. The European Commission says that elements of the asylum policy not being implemented include legislation focused on speeding up asylum decisions, ensuring humane treatment of asylum-seekers and clarifying grounds for granting asylum. European Commission First Vice President Frans Timmermans says, "Our common European asylum system can only function if everyone plays by the rules." Slovakia's prime minister says his country is challenging a European Union decision to redistribute 120,000 asylum seekers. Besides the legal complaint at an EU court in Luxembourg, Robert Fico says his country is not ready to accept the plan to share the burden of migrants across the EU. Czech Prime Minister Bohuslav Sobotka, who opposed the EU's quota scheme to relocate 120,000 asylum-seekers in member states, says he won't take legal action against the plan. Cameron met French President Francois Hollande late Tuesday, and Cameron's office says they "agreed that EU countries should do more to return migrants who don't have a genuine claim for asylum to their countries of origin." Deeply divided European Union leaders have been called to an emergency summit to seek long-term responses to the continent's ballooning crisis of refugees and migrants, a historic challenge EU President Donald Tusk said the bloc has failed dismally to meet. In a letter to presidents and prime ministers of member states, Tusk writes: "There is a long list of issues where we could blame one another, but it will not help us in finding a common solution." Slovak media used strong words to express bitter feelings after European Union interior ministers approved a plan to relocate 120,000 asylum-seekers .