Federal legislators are grilling U.S. and Puerto Rico officials on why power has not been fully restored to the island nearly eight months after Hurricane Maria as frustration builds in the U.S. territory.

Lawmakers at a Tuesday hearing of the U.S. Senate Committee on Energy & Natural Resources also questioned why the U.S. Army Corps of Engineers is pulling out of Puerto Rico next week.

The concerns come as the Caribbean prepares for the June 1 start of the new hurricane season and as the new CEO of Puerto Rico's power company is warning that restoring power to the more than 22,000 customers that remain in the dark has become increasingly difficult because of where they're located.

The Category 4 storm destroyed up to 75 percent of distribution lines.