Congressional Democrats on Friday took aim at Puerto Rico’s role as a tax haven, asking the U.S. Treasury to investigate if the struggling island is helping the wealthy dodge federal and state taxes with little apparent benefit to the local economy.

In a letter to Treasury Secretary Steven Mnunchin, four representatives asked for information regarding two Puerto Rican tax incentives, Acts 20 and 22, that were passed in 2012 with the goal of luring wealthy individuals and service-providing companies to the island.

Beneficiaries of the measures pay virtually no local income tax if they reside in Puerto Rico at least half the year; in addition, most Puerto Rican residents are exempt from federal income tax.