By Dave Graham

MEXICO CITY (Reuters) - A Mexican senator is proposing legislation to empower the government to retaliate if a U.S. administration led by Donald Trump inflicts expropriations or economic losses on his country to make it pay for a border wall.

Republican presidential nominee Trump has vowed to have Mexico fund the planned wall to keep out illegal immigrants if he is elected, and threatened to fund it by blocking remittances sent home by Mexicans living in the United States.

Armando Rios Piter, an opposition senator for the center-left Party of the Democratic Revolution (PRD), will next week present the initiative he hopes will protect Mexicans, and highlight the risks of targeting them economically.

The plan offers a taste of the kind of tit-for-tat measures that could gain traction between the two heavily-integrated economies if Trump wins the presidency at the Nov. 8 election.

In a preliminary summary of the proposal, which also foresees giving the Senate the power to disavow international treaties when the interests of Mexico or its companies are threatened by other signatories, it states:

"In cases where the property/assets of (our) fellow citizens or companies are affected by a foreign government, as Donald Trump has threatened, the Mexican government should proportionally expropriate assets and properties of foreigners from that country on our territory."

Total remittances to Mexico from abroad - most of which come from the United States - were worth nearly $25 billion last year, according to the central bank. Bilateral trade between the two nations is worth about half a trillion dollars a year.

Trump has also threatened to tear up a trade deal with Mexico if it is not recast in the United States' favor. He met President Enrique Pena Nieto in Mexico City this week, sparking fierce criticism in Mexico of the government for hosting him.

Afterwards, Trump repeated his pledge to make Mexico foot the bill for the wall. Mexico says it will not pay.

It is yet to be established how such expropriations could work, nor is it clear what chance the bill could have of passing. The PRD and other leftist parties hold less than a quarter of the 128 seats in Mexico's Senate.

Rios Piter said his aim was to counter threats by Trump to target Mexicans in the United States and to stress that the economic welfare of both nations is at stake.

"At a time like this, it's vital for us to understand why this relationship benefits both. We're neighbors, we're friends, we're partners," he said. "He's putting (that) at risk."

The initiative also seeks to protect Mexico against unilateral changes to the 1994 North American Free Trade Agreement (NAFTA), which Trump has threatened to ditch.

(Editing by Alistair Bell)