The Attorney General of Puerto Rico, Guillermo Somoza-Colombani, announced Friday that his territory had joined the Justice Department's lawsuit to block the merger of AT&T and T-Mobile.
Seven state attorneys general have also joined the lawsuit against the $39 billion deal.
Their case alleges the merger would violate antitrust law by stifling competition in the wireless market.
AT&T says the deal would benefit consumers and create jobs. The company has vowed to fight the lawsuit in court but has said it is willing to negotiate to address antitrust concerns.
Sprint and Cellular South have also filed suit against the merger of their rivals. AT&T filed motions to dismiss those cases Friday.