Zelaya will be accompanied home by Jose Miguel Insulza, the OAS secretary-general, the presidents of Argentina and Ecuador, and Miguel d'Escoto Brockmann, the head of the UN General Assembly.
But Roberto Micheletti, who was appointed interim leader by the Honduran congress just hours after the coup, has given warned that Zelaya will be arrested should he return, regardless of who is travelling with him.
Zelaya was forced by the military to go into exile in Costa Rica on Sunday.
Insulza said on Wednesday that he had delivered an "ultimatum" to Honduras after an emergency meeting of the OAS.
Speaking from the OAS headquarters in Washington DC, he said: "We need to show clearly that military coups will not be accepted.
"If within 72 hours the reinstatement doesn't happen, the assembly ... will meet again to suspend Honduras."
The move came hours after the General Assembly adopted a resolution calling for the "immediate and unconditional" return of Zelaya to the Honduran presidency.
The adoption of the General Assembly resolution on came as supporters of both Zelaya and his interim replacement demonstrated in the country's largest cities.
Al Jazeera's Monica Villamizar, reporting from San Pedro Sula, Honduras' commercial capital, said the protests were evidence that the coup had left the country deeply polarised.
"The police said for the moment that they have avoided a full-scale confrontation, but tensions are clearly mounting and anti-riot troops have cordoned off government buildings and shielded supporters of the military-installed government," she said.
"Zelaya supporters have called for a general strike until he returns. Many said he was a president who was helping the poor.
"But only blocks away, others said Zelaya was a threat to democracy, too easily influenced by left-wing governments like Venezuela and trying to modify the constitution to remain in power."
Meanwhile, Micheletti, who is a former parliamentary speaker from the same Liberal party as Zelaya, has vowed not to resign as interim president, saying that only an armed invasion would restore his ousted predecessor.
"No one can make me resign," Micheletti said.
"[Zelaya] can no longer return to the presidency of the republic unless a president from another Latin American country comes and imposes him using guns."
"I was appointed by congress, which represents the Honduran people. Nobody can make me resign unless I break the laws of the country," he told the Associated Press news agency.
Micheletti has insisted that Zelaya was not ousted through a coup but through "a completely legal process as set out in our laws", calling the move an "act of democracy".
Zelaya was removed from power as he was about to press ahead with a non-binding referendum on constitutional change on Sunday that congress and the courts had declared illegal, accusing him of trying to change the charter so he could run for a second term in office.
Before the General Assembly's condemnation on Tuesday of the coup, the overthrow of Zelaya had been roundly criticised by Latin American countries and the US.
Mariana Sanchez, Al Jazeera's correspondent in Honduras, said: "Spain and France have recalled their ambassadors. The US has joined its voice of condemnation with the UN.
"Although it has been a bit vague in qualifying what is going on here, Washington has a legal team analysing if this was a coup d'etat or not.
"The countries that border Honduras ... are considering closing their borders … Honduras is becoming a pariah country without any ties."
The US has not legally classified the removal of Zelaya as a coup as this would automatically lead to the suspension of aid to Honduras, an impoverished nation of 7.2 million people.
But the Pentagon on Wednesday suspended all military activities with Tegucigalpa until further notice.