As majority leader of the Senate, Nevada’s Harry Reid, is one of the most powerful people in Washington.Bloomberg

The nation’s top energy regulator may soon get two new leaders who share at least one thing in common: the unrelenting attention of Sen. Harry Reid.

As majority leader of the Senate, the Nevada Democrat is one of the most powerful people in Washington. Over the past year, he has on two occasions scotched the White House’s pick of leader for the Federal Energy Regulatory Commission, a low-profile agency that oversees the nation’s electric grid, and he has successfully pushed for other preferred candidates.

His efforts will be tested as soon as this week when the Senate’s energy committee votes on whether to confirm Norman Bay as FERC chairman and Cheryl LaFleur as a commissioner. Mr. Bay is a Reid-backed candidate. The senator blocked Ms. LaFleur from getting the top job, and he is blunt about his interest in shaping FERC.

“Oh really? No kidding,” Mr. Reid said. “Wow, that is amazing—that a majority leader who has a responsibility of selecting people would have some opinion as to who he suggests to the White House.”

Mr. Reid’s interest stems from his expressed intent to develop his state’s renewable-energy industry. In 2013, Nevada ranked second in the nation for geothermal energy production and third for solar production, and 18% of its total electricity generation came from renewable, above the national average of 13%.

Nevada and the West in general, however, need more power lines to deliver renewable energy to customers. While FERC, which can have as many as five members, doesn’t generally approve construction of interstate power lines, it does approve wholesale electric transmission sales and tariffs, which influence where power companies decide to build transmission lines.

Mr. Reid’s attentions have roiled an agency that, like other federal regulatory bodies, is supposed to be independent from Congress and the executive branch.

“The uncertainty over the makeup of the commission has created a level of dysfunction I have not seen in my five years on the commission,” said John Norris, an Obama commission appointee who also was boxed out of the chairmanship by Mr. Reid, according to people involved in the process. “The dysfunction of the Senate seems to be spilling over to those agencies Sen. Reid wants to have a controlling hand on.”

A spokeswoman for Ms. LaFleur declined to comment. A White House spokesman declined to address specific interactions with Mr. Reid.

“We, of course, work closely with Sen. Reid and other members of the Senate to nominate and confirm the best, most qualified candidate for open positions across the government,” said White House spokesman Matt Lehrich. “When it comes to FERC, the president chose Norman Bay because he is a proven leader and dedicated public servant with expertise in the energy markets, a tough, evenhanded approach to enforcing the law, and a history of bipartisan support.”

Mr. Norris was the first potential nominee for chairman to run into Mr. Reid. According to the people involved in the nominations process, the lawmaker insisted the White House not nominate Mr. Norris as chairman, in part because he had taken a position in a previous job that Mr. Reid considered too favorable to coal.

“It is a rare instance,” said one former Obama administration official. “Usually the White House and Sen. Reid work together pretty well. This was a bit of hard ball.”

Mr. Reid wanted instead someone from a Western state similar to Nevada, according to people familiar the matter. (Mr. Norris is an Iowan).

Last July, the White House nominated former Colorado Public Utilities Commission Chairman Ron Binz as chairman. A few months later, Mr. Binz withdrew his nomination because of opposition from Republicans and some Democrats for comments he made about supporting renewable energy over fossil fuels.

Mr. Reid also didn’t take to Ms. LaFleur as chairman, contending she wouldn’t adequately protect consumers from electricity-market manipulation or support building transmission lines for renewable energy. “I don’t want her as chair,” Mr. Reid said during a recent interview in his Washington office.

Ms. LaFleur has been acting chairman since Jon Wellinghoff, a Nevadan close to Mr. Reid, retired in late 2013. “She has done some stuff to do away with some of Wellinghoff’s stuff,” Mr. Reid said.

Mr. Bay is up for a vote as FERC chairman by the Senate committee as soon as Thursday, after which the full Senate would vote. Mr. Reid supports him in large part because he hails from a Western state, New Mexico. He also draws bipartisan support.

It isn’t rare for lawmakers to work to shape regulatory agencies, but observers said Mr. Reid’s direct line to the White House allows him to fight for who he wants on FERC behind the scenes. The senator’s allies also say Washington lawmakers routinely seek to benefit the states they represent.

“You’re crazy not to use it to help your constituents back home,” said Eric Washburn, a principal at lobbying firm Bracewell & Giuliani who worked on energy and environment issues for Democratic senators, including Mr. Reid, for 10 years. “People may argue that is unfair, but it is the seniority system and it is what it is.”

Mr. Reid’s vision for FERC is broadly aimed at securing investment in renewable energy and transmission lines in the West.

He helped secure federal approval for a major renewable-energy power line in Nevada, according to former Reid aides, and supported the sale of Las Vegas-based utility NV Energy to a unit of Berkshire Hathaway Inc. BRKB -0.51% The merger, which FERC approved in December a month after Mr. Wellinghoff left, has opened the door for more renewable-energy investments in Nevada, the company has said.

FERC under Mr. Wellinghoff advanced policies that in the long run help boost Nevada’s renewable energy, according to Mr. Reid and his aides. One regulation that FERC approved in 2011 under Mr. Wellinghoff requires states to coordinate on transmission planning, such as new power lines, which utility experts say would help move renewable energy more easily, especially throughout the West.

“Sen. Reid understands and appreciates the tremendous opportunities that there are for Nevada to develop its own renewable energy resources,” Mr. Wellinghoff said. “And he supports Nevada becoming an exporter of these resources.”