Democratic presidential candidate Bernie Sanders is breaking with the Obama administration and House lawmakers over a plan to restructure Puerto Rico's $70 billion in debt, saying the legislation would make "a terrible situation even worse."

The Vermont senator writes in a letter released Monday that the deal reached last week between the White House and House Republicans and Democrats would empower an "unelected and undemocratic oversight board" and allow the governor of Puerto Rico to slash the minimum wage to $4.25 an hour for up to five years.

"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 letter to Senate colleagues.

"At a time when the people of Puerto Rico are suffering, the legislation introduced in the House would make a terrible situation even worse," he wrote.

Sanders trails Democratic rival Hillary Clinton in the presidential primaries and both are competing in the upcoming June 5 Puerto Rican caucuses. Clinton has outperformed Sanders among Latino voters during the primaries.

Sanders has been virtually absent from Senate proceedings during his lengthy primary campaign but his opposition could complicate the measure's future after careful negotiations between the White House and House Speaker Paul Ryan.

Ryan, R-Wis., has said the bill would avoid an eventual taxpayer bailout and Treasury Secretary Jack Lew has called it a "tough bipartisan compromise." House Democratic leader Nancy Pelosi also supports the agreement.

Puerto Rico, which has struggled to overcome a lengthy recession, has missed several payments to creditors and faces a $2 billion installment, the largest yet, on July 1. Two government agencies have been under a state of emergency and many businesses have closed, schools have lacked sufficient resources like electricity and some hospitals are limiting treatment.

Sanders warned that the control board would have the power to cut the budget, slash pensions and take other measures. He notes that most of the control board would be chosen by Ryan and Senate Majority Leader Mitch McConnell, R-Ky.

Puerto Rican officials have argued for a less powerful board that could not control the island's finances.

Republicans say the legislation would force the control board to both consider creditors and also find a way to fund pensions. The Puerto Rican government has underfunded pensions by more than $40 billion.

Sanders said the legislation "looks out for the needs of Wall Street vulture funds first and foremost. That is unacceptable."