Jordan's PM has said annexing parts of the West Bank will force the country "to review all aspects of our relations with Israel".
Israeli plans to annex swathes of the West Bank would violate its peace treaty with Jordan, heaping pressure on Amman to review its ties with the Jewish state, analysts say.
But ultimately cash-strapped Jordan, which depends on over a billion dollars in annual aid from the US, will be unable to stop the move, which has been greenlighted by Washington, they say.
Jordan is, along with Egypt, the only Arab nation to have signed a peace treaty with Israel.
'Considering all options'
But opinion polls have repeatedly shown that the 1994 treaty, signed one year after Oslo peace accords between Israel and the Palestinians, is overwhelmingly opposed by Jordanians.
King Abdullah II, who has often complained of a "cold peace" with Israel, has already warned that annexation would lead to a "massive conflict".
"I don't want to make threats and create a loggerheads atmosphere, but we are considering all options," the king told German magazine Der Spiegel in May.
Ordinary Jordanians, meanwhile, told AFP it poses an "existential threat" for a country where more than half of the 10 million population are of Palestinian origin.
Jordan would be "forced to review all aspects of our relations with Israel", Prime Minister Omar al Razzaz has said.
Analysts say there are many options on the table.
Jordan could cancel the peace treaty or scrap some of its key clauses, namely those concerning security and intelligence cooperation, shutter Israel's embassy in Amman or recall its ambassador from Tel Aviv.
"Jordan must send a decisive message to Israel and the Americans that says if you take that path (annexation) we will cancel the peace treaty," said Oraib Rintawi of the Al-Quds Centre for Political Studies.
Former Jordanian information minister Mohammed al-Momani said Israel's planned annexation of Jewish settlements and other territory in the West Bank, including the Jordan Valley that runs along Jordan's border, would be a clear "violation" of the peace treaty.
The treaty stipulates that "no side will take unilateral action that will undermine the interests of the other side". But annexation "undermines Jordanian interests, which lie in the creation of a Palestinian state," he said.
"This is a direct threat to Jordan's national security," added Momani, saying Amman could urge UN Security Council intervention or complain to the International Court of Justice.
Analysts say Jordan signed the peace treaty specifically because it believed it would pave the way for the creation of a Palestinian state and solve a problem that has bedevilled the kingdom for decades.
Sandwiched between Israel and Jordan, the West Bank, including east Jerusalem, had been under Jordanian administration until Israel occupied it in the 1967 Six-Day War.
Following the conflict, hundreds of thousands of Palestinians fled to Jordan to join an influx of others who sought refuge there after the creation of Israel in 1948.
Jordanians of Palestinian origin account for more than half of Jordan's 10 million people and 2.2 million Palestinians are registered with the United Nations as refugees.
Palestinians say annexation would make it impossible to form a coherent Palestinian state with east Jerusalem as its capital.
King Abdullah shares that view and has repeatedly said there can be no alternative to a Palestinian state and no permanent settlement of Palestinian refugees in Arab host countries.
On the streets of Amman, Jordanians questioned by AFP echoed the king's views and expressed their own fears.
"The annexation plan is an existential danger for Jordan and Palestine," said shopkeeper Abdullah Musa, 44, who sells electrical appliances.
"There will be nothing left to establish a Palestinian state," he said.
Photographer Luay Malhass said "tens of thousands of Palestinians will be forced to flee the West Bank".
"Annexation ... will create a dilemma for Jordan by forcing on it the option of an alternative state for the Palestinians and their permanent settlement," Malhass said.
Cancelling the peace treaty with Israel would be the king's "most important decision of his reign", Musa added.
But some analysts believe Jordan's ability to stand up against the US-backed Israeli plans is limited.
"Jordan's options will be diminished because it is bound by strategic relations with Washington ... and is very much dependent on US aid," said Ahmad Awad, head of the Phoenix Centre for Economics and Informatics Studies.
Kirk Sowell, analyst with Utica Risk Services, believes Jordan will not confront Israel.
"Jordan can suspend the treaty if it wishes ... (but) Jordan is not going to do anything tangible to stop annexation," he said.
It could also "formally suspend security cooperation ... but security cooperation would continue, informally, because Jordan cannot survive otherwise", he added.
Even suspending the gas agreement between the two countries would hurt Jordan more than Israel.
"There will be lots of rhetoric about opposition to it, but there is nothing Jordan can do," he said.