Democratic presidential candidate Bernie Sanders called on Senate Democrats to oppose a broadly supported bill to help Puerto Rico handle its debt crisis.

{mosads}The Vermont senator said Monday the bill “would make a terrible situation even worse,” citing concerns with a control board the legislation sets up. 

“We must stop treating Puerto Rico like a colony and start treating the American citizens of Puerto Rico with the respect and dignity that they deserve,” Sanders wrote in a Monday letter to Senate Democrats.

Sanders announced his opposition to the new Puerto Rico Oversight, Management and Economic Stability Act (PROMESA) on Thursday. 

An updated version of PROMESA was introduced last Wednesday. It’s supported by House Speaker Paul Ryan (R-Wis.), House Minority Leader Nancy Pelosi (D-Calif.) and Democratic presidential front-runner Hillary Clinton.

Puerto Rico holds its Democratic presidential primary on June 5.