CARACAS (Reuters) - Venezuela’s opposition alliance called on the United Nations on Monday not to send observers to the presidential election on May 20 to avoid legitimizing a poll it says is rigged in favor of Socialist President Nicolas Maduro.

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Maduro, who is seeking re-election amid an economic collapse that has sent a tide of migrants to neighboring countries, has asked the United Nations to send observers to the vote.

The main opposition coalition is boycotting the election on the grounds that the elections council has historically favored the ruling Socialist Party, and because the best-known candidates have been jailed or barred from holding office.

“What we have asked the United Nations today is not to validate the electoral fraud in May,” said legislator Delsa Solorzano of the Broad Front coalition at a small demonstration outside a U.N. office in Caracas.

She added that any U.N. mission should “be only for human rights issues, not to validate a dictatorship.”

A U.N. spokesman contacted via email said the government’s request for a mission had been received.

“But our position on all such matters is that the sending of electoral observers requires a mandate from one of the UN’s Member State bodies” such as the Security Council or General Assembly, wrote spokesman Farhan Aziz Haq.

“If the (General Assembly) or the Security Council were to provide a mandate, we would respond accordingly. But neither has done so up until now.”

Opposition leaders are planning a protest on Saturday to demand better conditions for the upcoming vote.

Former state governor Henri Falcon has broken with the coalition and will run against Maduro, insisting that Maduro’s low opinion poll numbers make him a weak candidate. Critics say the government is likely to manipulate the vote results and that participating will legitimize the process.

Maduro says his government is the victim of an “economic war” led by the opposition with the help of Washington. His critics say the country’s problems are the result of dysfunctional socialist policies.