Porfirio Lobo came to power after the military overthrew his predecessor
South American leaders have threatened to pull out of a scheduled EU-Latin American summit in Spain if Honduras President Porfirio Lobo attends.
Some leaders of the 12-nation South American Unasur bloc urged Spain to revoke Mr Lobo's invitation.
Venezuela's Hugo Chavez and Brazil's Luiz Inacio Lula da Silva were among the leaders backing the move.
They still refuse to accept Mr Lobo's government because of the way his predecessor, Manuel Zelaya, was ousted.
Mr Zelaya was forced out amid a dispute with the country's Congress and the courts over his plans to hold a non-binding public consultation to ask people whether they supported moves to change the constitution.
An interim government was set up to steer the country through to an election which had been scheduled before the overthrow.
Mr Lobo won that election, but the legitimacy of his government remains a contentious issue in Latin America.
Earlier this week the Spanish government, which currently holds the EU presidency, invited Mr Lobo to the EU-Latin America summit, scheduled to begin on 18 May.
"There is unease shared by most of us that will prevent a lot of Unasur countries attending the summit," said Ecuadorian President Rafael Correa, according to AFP news agency.
Venezuelan President Hugo Chavez added: "We don't want to boycott the summit. We want Spain to come to its senses."
An aide to Brazil's President Lula, Marco Aurelio Garcia, said: "If Honduras attends, then at least 10 Latin American presidents will not go to Madrid, starting with the president of Brazil."
The Unasur bloc was formed nearly two years ago to boost unity among the region's powers and counterbalance the perceived influence of the US.
But correspondents say its goals of development and democracy-building remain far off.
Unasur is made up of Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Guyana, Paraguay, Peru, Suriname, Uruguay and Venezuela.