It is shaping up as a hectic summer for investors in Puerto Rico’s more than $70 billion in outstanding debt.

On Monday, the U.S. commonwealth’s publicly owned electric monopoly presented creditors with a restructuring plan, a month before a roughly $400 million payment comes due that analysts say the utility doesn’t have.

The plan includes efforts to modernize the authority and increase efficiencies, with a goal of stabilizing power rates, according to Chief Restructuring Officer Lisa Donahue, who declined to talk about a possible debt restructuring, citing continuing confidential talks with creditors.

The power authority, known as Prepa, is negotiating with creditors ahead of a June 4 deadline to extend talks or face a possible default. Prepa has been drawing on reserves to make debt payments and doesn’t have enough in those accounts to make the July payment, its trustee said in an April bond disclosure.

The episode highlights the volatility of Puerto Rico’s fiscal situation as the commonwealth and its indebted public agencies face a series of deadlines in coming weeks, each of which has the potential to change investor attitudes toward the island’s debt.