The foundation run by US billionaire George Soros said Monday that it has filed a legal challenge with the European Court of Human Rights in Strasbourg against Hungary's controversial "Stop Soros" laws adopted last June.
The New York-based Open Society Foundations (OSF) said in a statement that it had submitted a complaint to the rights court, calling on it to "defend Hungarian democracy" and urge a repeal of the laws.
"There is only one thing this legislation will stop and that's democracy," said OSF president Patrick Gaspard.
The "Stop Soros" package targetting the Hungarian-born 88-year-old includes a 25-percent tax on non-governmental organisations (NGOs) deemed to be supporting or positively portraying migration.
A year's prison term could also be handed to those convicted of assisting someone to enter the country illegally.
According to OSF lawyer Daniela Ikawa, the measures breach EU conventions on freedom of speech and association, and expose "a broad range of legitimate activities to the risk of criminal prosecution".
The foundation moved a regional office from Budapest to Berlin last month citing what it called the "repressive" policies of nationalist firebrand Prime Minister Viktor Orban.
In April, Orban won a landslide victory in an election that handed him a third straight term as prime minister. He has since indicated he wants to use this mandate to intensify his anti-migrant, nationalist and culturally conservative agenda.
Anti-immigrant rhetoric was a key part of Orban's election campaign.
His government accuses Soros of using his organisations to orchestrate immigration and undermine the cultural and religious identity of Europe.