ASUNCION (Reuters) - Security forces surrounded Paraguay’s Congress on Tuesday while lawmakers argued over a possible change in law that would allow President Horacio Cartes to run for re-election, a move that the opposition says would weaken democratic institutions.

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Hundreds took to the streets of the capital in opposition-led protests of the proposed change, though no incidents of violence were reported. Police remained outside the building well into the evening, and streets surrounding the Congress and presidential palace remained closed off.

A bill allowing presidents to run for a second five-year term was defeated in the legislature last year.

This week a group of senators asked for a special session that the opposition interpreted as the start of a new campaign by Cartes and his coalition to enable presidential re-election.

That request was formally rejected on Tuesday, but Senator Julio Cesar Velazquez, a Cartes ally, convened a special session anyway with a group of legislators. They approved procedural changes that could pave the way for allowing presidential re-election.

Opposition leaders labeled this a “parliamentary coup” and filed a complaint with the country’s attorney general.

“We have to safeguard the republic,” said Senator Blanca Ovelar, a member of Cartes’ Colorado Party who has broken with the president. “This is a situation of institutional breakdown.”

Soft drink and tobacco mogul Cartes was elected to a five-year term in 2013. His strongest backers want him to be allowed to run for another term next year. Critics say a constitutional change aimed at benefiting a sitting president would be unfair.

The Inter-American Development bank is holding a regional meeting in Asuncion starting on Thursday. Security consultancies International SOS and Control Risks issued a statement warning conference goers to avoid the vicinity of the Congress building in case tensions escalate.

On Wednesday, thousands of subsistence farmers are expected to come to capital city Asuncion to lobby for agrarian reform. Protests in favor of more protections for small farmers are held at Congress every March.