PORT-AU-PRINCE (Reuters) – Some of Haiti’s sitting legislators have vowed to block newly elected senators from taking office, in a protest against the exclusion from the ballot of candidates from one popular party.

The move could create more political division and instability as the Caribbean nation struggles to attract new investments at a time of great economic hardship.

An election was held in two rounds on April 19 and June 21 to fill 11 seats in Haiti’s Senate and results from the second round are expected to be released soon.

Election authorities had barred candidates from former President Jean-Bertrand Aristide’s Lavalas Family party from the ballot, alleging the party failed to submit required legal papers to register candidates.

The Lavalas Family party, the country’s biggest political force, accused the electoral council of bias and of conspiring against it and said such papers had never been required in previous elections. The party called for a boycott and both rounds of voting were marked by a record low turnout.

International donors, such as the United States, Canada and the European Union, provided more than $11 million of the $16 million cost of holding the election.

Yvon Buissereth and Rudy Heriveaux, both senators from Aristide’s party, and three other colleagues said they will boycott the validation process of the 11 newly elected senators.

“We warned Haitian authorities and the international community that supporting financially the organization of such an election was a waste of money,” Buissereth told Reuters in a week-end interview. “We are going to prove it.”

Haiti’s constitution requires incumbents to validate, during a full session, the powers of incoming colleagues before they can be sworn in and take office.

Eighteen incumbents hold office in the 30-member Senate and at least 16 senators must be present to hold any session. If the five senators carry out their boycott threat, they can block a validation session.