A Federal Energy Regulatory Commission member resigned Friday, adding to agency vacancies that already have put roughly $10 billion in natural gas pipeline projects in limbo and further highlighting President Trump’s challenges to fill appointments and get his administration fully staffed.

Colette Honorable, a Democrat, says she will not seek reappointment after her term expires in June, leaving the five-member panel with just one commissioner.

The agency hasn’t had the minimum three members to vote -- known as a quorum -- since February when Democrat Norman Bay resigned.

That situation has prevented the agency from ruling on the $10 billion worth of projects, a total spread over roughly a half-dozen separate projects.

FERC regulates the transmission and interstate commerce of wholesale electricity and natural gas. The agency also regulates the interstate transportation of oil by pipeline and reviews related proposals including those for natural gas pipelines.

Honorable is not saying when she will leave and could stay until replaced or until Congress adjourns next year.

Those nominated by a president to be a FERC commissioner must receive Senate confirmation.

Much of the attention on Trump’s appointments early in his presidency has focused on the Cabinet and Supreme Court level. But hundreds of key but lower-level appointments remained unfilled.

“It’s not just FERC," Max Stier of the nonpartisan Partnership for Public Service's Center for Presidential Transition. “The government is a big place, and understanding its many corners is a big part. It has major implications for our country."

Stier also points to a similar situation at the federal Merit Systems Protection Board, which hears appeals from federal employees who have been fired or faced other strong disciplinary action.

The agency also doesn’t have enough members to make decisions on cases, amid bipartisan calls to have appointees promptly named and approved.

“It’s not that the board cannot go faster,” Stier told Fox News on Saturday. “It cannot go at all. It has created the inefficiencies that President Trump is trying to change.”

Lawmakers from both parties have expressed alarm at the prolonged FERC vacancies. Alaska Sen. Lisa Murkowski, chairwoman of the Senate Committee on Energy and Natural Resources, has pressed the White House for months on the issue.

The Alaska Republican called Honorable "a true champion of the increasingly important work of this independent agency," adding that her expertise has strengthened the commission.

"It is imperative that a quorum is restored as expeditiously as possible,” she said. “This continues to be a top priority for me, and a hearing will be scheduled as soon as we receive nominations and the proper paperwork."

The Associated Press contributed to this report.