More than 1,000 European lawmakers from 25 countries urged their leaders Wednesday to step in and stop Israel's planned application of sovereignty over parts of Judea and Samaria.
Israeli Prime Minister Binyamin Netanyahu intends to kick-start the process next week, after clinching a coalition deal with his former election rival last month.
In a letter published in newspapers and sent to European foreign ministers, the 1,080 parliamentarians said they were "deeply worried about the precedent this would set for international relations".
"Such a move will be fatal to the prospects of Israeli-Palestinian peace," added the letter.
"Regrettably, President (Donald) Trump's plan departs from internationally agreed parameters and principles."
The letter referred to the US leader three times but made no direct mention of Netanyahu, who must still decide how much territory he intends to place under Israeli law.
"In appreciation of Europe's long-term commitments to the peaceful resolution of the Israeli-Palestinian conflict, we ask European leaders to act decisively in response to this challenge," the lawmakers said.
"Europe must take the lead in bringing international actors together to prevent annexation."
The European Union has been seeking to persuade Israel to back down and is weighing retaliatory measures as a response if Netanyahu goes ahead.
However, mooted sanctions would require the agreement of all 27 member states.
Most of the signatories of the MPs' letter were members of left-leaning parties and nearly a quarter came from Britain -- which left the EU in January -- including the Labour party's foreign affairs spokeswoman Lisa Nandy.
Britain's main opposition party is trying to recover from years of controversy over anti-Semitism within its ranks.