A referendum on how many chambers the Legislative Assembly should have was held in Puerto Rico on July 10, 2005. The proposed change to a unicameral legislature was supported by 83.94% of those voting, although voter turnout was just 22.58%. However, another referendum would have to be held to approve the specific amendments to the constitution that are required for the change. The House of Representatives subsequently let the bill die, so the changes were not realised. Had the changes been approved, the legislature would have become unicameral from 2009 onwards.
The Puerto Rican Independence Party supported the victorious "yes" vote in favor of one chamber. The Popular Democratic Party did not take an official stance on the matter, with its leadership supporting or opposing the measure. The New Progressive Party opposed the constitutional amendment under electoral review, but supported abstention from the vote.