Panama's President Martin Torrijos has authorized holding a referendum October 22 on whether to expand the nation's canal.
Mr. Torrijos signed the measure Monday, two days after lawmakers agreed to the vote on the more than $5-billion project.
The plan would add a third set of locks to the canal to increase traffic and to allow larger vessels to transit between the Atlantic and Pacific oceans.
Officials say they plan to raise tolls at the canal and seek loans to finance the expansion.
Some Panamanian workers' unions say they oppose the building project, saying more money should be spent on social development.
Panama took over administration of the canal from the United States in 1999.
Some information for this report was provided by AP.