"The decision to move operations out of Budapest comes as the Hungarian government prepares to impose further restrictions on non-governmental organizations through what it has branded its "Stop Soros" package of legislation", it continued.
"The Foundations will pursue all available legal avenues to defend the fundamental rights that are threatened by the legislation", OSF said in the statement, vowing to continue the organisation's work in Hungary through funding from the German capital.
Open Society Foundations is closing its operations in Hungary and moving staff to Berlin, citing an increasingly repressive political and legal environment and security concerns.
Hungarian Prime Minister Viktor Orban has blamed Soros, a Hungarian-born US financier, for a host of ills and is planning to tighten a crackdown on non-governmental organizations (NGOs) under legislation dubbed the "Stop Soros" bill.
But it would move its Budapest-based global operations and staff to Germany.
On Monday, Antal Rogan, the minister for Orban's cabinet office, said the government would propose a "tighter" Stop Soros bill without providing any details.
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OSF said it would still support the work of civil society groups in Hungary after it had left.
Orban has increased his control over the media and put allies in control of formerly independent institutions, while his stand on refusing to accept large numbers of migrants in Hungary has also put him in conflict with the EU.
Poland's Prime Minister Mateusz Morawiecki meets his Hungarian counterpart Viktor Orban in Warsaw, Poland May 14, 2018.
Orban has accused Soros of being a part of a technique to flood Europe with migrants and of meddling in home affairs. The Hungarian government opposes the Open Society's open immigration policies.
The government has repeatedly denied this.
Another term for Orban could also have implications for Soros's Central European University, a graduate school which is considered by the government a foreign institution.