On Monday, Orban's cabinet minister Antal Rogan said the government would further tighten restrictions on non-governmental organizations in its planned "Stop Soros" bill.
"The government of Hungary has denigrated and misrepresented our work and repressed civil society for the sake of political gain, using tactics unprecedented in the history of the European Union", OSF president Patrick Gaspard said in a statement.
As well as bemoaning "burdensome" transparency requirements on funding from overseas, the group registered its particular anger over measures in the package invoking national security interests, such as rules which would require NGOs working with asylum seekers to be licensed by the government.
Hungarian-American financier George Soros" "Open Society Foundations' network - which funds liberal causes such as the defense of human rights, education, criminal justice reform and better public health standards - announced Tuesday that it will close their offices in Budapest over government legislation targeting its efforts.
Orban is leveraging his recent massive electoral victory to restrict the political influence of NGOs, many of which received millions from Soros, a Hungarian who escaped the country before Nazis invaded.More news: Former A&M standout Christian Kirk arrested for disorderly conduct before National Football League draft
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"Orban now wants to enact laws that force non-governmental organizations (NGOs) to register with the government".
Soros has remarked that the Hungarian government was attempting to slander him by pushing "distortions and lies". "It has become impossible to protect the security of our operations and our staff in Hungary from arbitrary government interference", CNBC added.
The foundation backed by the Hungarian-born USA billionaire is set to move its staff to the German capital of Berlin.
Orban's campaign for the April election vilified Soros and his activities in support of civil society on billboards nationwide, and he made clear he would be glad to see the OSF leave Hungary. Foreign funding for activities related to migration would be subjected to a 25 percent tax.
The prestigious Soros-founded Central European University is also waging a battle against Orban after a higher education law was passed past year that it says threatens its survival in Hungary.