Israel is set to become the first democracy to expel a Human Rights Watch employee, its executive director Ken Roth said on Sunday.
US citizen Omar Shakir, director for Israel and the Palestinian territories for the rights group, is to be deported from Israel on Monday over his alleged support of a boycott of the Jewish state.
Mr Shakir would be the first to be expelled under a controversial 2017 law allowing the deportation of foreigners who support a boycott, authorities say.
HRW denies Mr Shakir supports a boycott and accuses Israel of seeking to suppress criticism of its policies towards Palestinians.
"I cannot think of another democracy that has barred a Human Rights Watch researcher," Mr Roth told AFP in Jerusalem.
Mr Roth said countries including North Korea, Venezuela and Iran had expelled the group's researchers but no functioning democracy had taken such action.
"I think it demonstrates the increasingly constrained nature of Israeli democracy," he said.
Mr Roth said that Israel, despite having elections and a free press, tried "as much as it can" to silence efforts "spotlighting the human rights violations at the heart of the oppressive, discriminatory occupation" of Palestinian land.
Mr Shakir has fought a long legal campaign against expulsion but this month Israel's Supreme Court upheld the government's deportation order.
Israel accuses him of supporting the banned Boycott, Divestment and Sanctions (BDS) movement, which calls for a wide embargo 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.
Supporters compare it to the economic isolation that helped to bring down apartheid South Africa.
"All those who work against Israel must know that we will not let them live or work here," Interior Minister Aryeh Deri said this month.
The UN and EU have criticised the expulsion and called on Israel to cancel it.
But the US would say only that it supported freedom of expression worldwide.
Mr Roth contended that US President Donald Trump's support for Israel's right-wing government emboldened it to crack down on human rights groups.
"It is hard to imagine Omar's deportation going ahead if the US government hadn't given a kind of implicit green light," he said.
The case against Mr Shakir was initially based on statements he made in support of a boycott before taking up his post with HRW.
But the government case highlighted comments he has made since joining the rights group, including criticism of Israeli settlements in the occupied West Bank.
Mr Shakir said he had not called for a boycott in his capacity as HRW's representative in Israel, but said the rights group did not restrict free speech, including the right to call for a boycott.
"It is undeniable that boycotts around the world have led to changing unjust systems but Human Rights Watch doesn't take a position on them," he said on Sunday.
The organisation said Mr Shakir would continue in his position despite being expelled, working from neighbouring Jordan.
Mr Roth said that while Israel claimed the issue was Mr Shakir, authorities took issue with HRW highlighting Jewish settlements, which are considered illegal under international law.
"So we couldn't possibly replace Omar, because whoever the next person would be would engage in the same kind of advocacy that just led to Omar's deportation," he said.
