A government billboard is seen in Budapest, Hungary, February 14, 2018. A billboard reads: 'Soros wants to transplant millions from Africa and the Middle East'. REUTERS/Bernadett Szabo

GENEVA (Reuters) - The United Nations on Friday labeled an anti-immigration law proposed in Hungary an “assault on human rights” and urged its government to uphold the right of freedom of association.

The nationalist government in Budapest on Tuesday submitted legislation to parliament that would empower the interior minister to ban non-governmental organizations (NGOs) that support migration and pose a “national security risk”.

The bill is part of an anti-immigration drive by Prime Minister Viktor Orban that has set its sights on a campaign by Hungarian-born financier and philanthropist George Soros to bolster liberal and open-border values in eastern Europe.

It appeared to mark a further tightening of controls on groups “working on issues the government regards as against state interests, such as migration and asylum”, U.N. human rights spokesman Rupert Colville said.

It represented “an unjustified restriction on the right to freedom of association and is a worrying continuation of the government’s assault on human rights and civic space,” he told a Geneva news briefing.

The government says the bill, which would also impose a 25 percent tax on foreign donations to NGOs that back migration in Hungary, is meant to deter illegal immigration Orban says is eroding European stability and has been stoked in part by Soros, who has dual Hungarian and U.S. citizenship.

“Such a tax is likely to result in reduced budgets and disrupt fundraising, thereby undermining NGOs’ ability to carry out their activities and services,” Colville said.