Israel's supreme court on Tuesday upheld a government decision to expel a senior Human Rights Watch official over his alleged support of a boycott of the country, the ruling said.
Israel has sought to expel Omar Shakir, the New York-based rights group's director for Israel and the Palestinian territories, for more than a year.
It will now be up to the government whether to follow through and deport Shakir, a US citizen, who brands the move a bid by Israel to silence and delegitimise critics of its treatment of the Palestinians.
"If it proceeds, I have 20 days to leave & (Israel will) join ranks of Iran, N Korea & Egypt in blocking access for @hrw official," Shakir tweeted after the decision was announced.
It would be the first expulsion of its kind under a 2017 law allowing the deportation of foreigners who support boycotting Israel, although there have been cases of people being denied entry under the measure.
Israeli Interior Minister Aryeh Deri said he was "delighted that the supreme court this morning has validated my decision to not extend the visa of Omar Shakir, one of the leaders of the BDS (Boycott, Divestment and Sanctions) movement, for his support for boycotting Israel."
"All those who work against Israel must know that we will not let them live or work here," he added.
HRW said it urges businesses to stop operating in Israeli settlements in the occupied West Bank in order to avoid complicity in human rights abuses, but insisted it does not advocate a boycott of Israel itself.
It said it had "vigorously contested" claims Shakir had done so since joining the organisation.
Kenneth Roth, its executive director, condemned the court's decision and warned that more such rulings would follow.
"The supreme court has effectively declared that free expression in Israel does not include completely mainstream advocacy for Palestinian rights," he said.
"If the government now deports Human Rights Watch's researcher for asking businesses to respect rights as we do across the world, there's no telling whom it will throw out next."
The case against Shakir was initially based on alleged statements in support of a boycott he made "in the distant past", prior to taking up his post, HRW says.
The government later added new statements it alleges are in support of a boycott.
Israel's ministry of strategic affairs, which probes potential violations of the 2017 law, alleges Shakir's activism, particularly related to the country's occupation of the West Bank, has amounted to calls for a boycott.
The BDS movement calls for a broad-ranging boycott of Israel over its treatment of the Palestinians.
Israel sees the movement as a strategic threat and accuses it of anti-Semitism -- a claim activists strongly deny.