President Trump’s attempt to exert more control over the U.S. Postal Service has fueled concerns that those efforts could hurt the agency’s ability to reliably deliver mail to all corners of the country, a mandate that is core to its mission.

White House officials have said that Mr. Trump has no imminent plans to seize control of the Postal Service, which has operated as an independent agency for more than a half-century. But the president suggested on Friday that he would consider a major reorganization of the agency, which he has repeatedly criticized and tried to undermine for years.

Many see the effort as a way for the Trump administration to eventually try to privatize the Postal Service, which Mr. Trump previously said he was considering. That prospect has alarmed union officials, advocacy groups and Democratic lawmakers, who say that selling off or contracting out major aspects of the service could threaten thousands of postal worker jobs or drive prices higher for customers. Opponents also say the effort would disproportionately affect rural communities, where it is less profitable for private companies to deliver mail.

“We believe it would result in a death spiral for whatever is left,” said Brian L. Renfroe, the president of the National Association of Letter Carriers. “People in rural areas would be particularly hard hit.”

A takeover of the Postal Service could also revive concerns about whether the president could exert control over the delivery of mail-in ballots during national elections. In 2020, when voting by mail spiked during the pandemic, Mr. Trump’s political adversaries accused him of purposely trying to manipulate delivery of ballots in Democratic areas.

Millions of Americans vote by mail, relying on the post office to deliver their ballots by the voting deadlines.

On Friday, Mr. Trump said the White House would be looking at a “form of a merger” to turn around the Postal Service’s financial losses, although he said the agency would “remain the Postal Service.” Mr. Trump said that Commerce Secretary Howard Lutnick, who had a “great business instinct,” would help with the effort.

“We want to have a post office that works well and doesn’t lose massive amounts of money,” Mr. Trump said. “I think it’ll operate a lot better than it has been over the years. It’s been just a tremendous loser for this country.”

Mr. Trump’s comments came after The Washington Post reported last week that he was preparing to issue an executive order that would fire members of the agency’s governing board and shift the Postal Service under the Commerce Department.

For Mr. Trump, the Postal Service is a politically rich target to go after. Its employees are mostly unionized workers who have aggressively campaigned against privatizing America’s delivery of the mail.

The administration’s desire to shake up the Postal Service comes as the agency continues to face persistent financial challenges and declining mail volume. In the 2024 fiscal year, the service lost $9.5 billion, up from $6.5 billion the year before. The agency has recently seen more promising financial results, however, posting a profit for the first quarter of the fiscal year.

Legal and postal experts said the Trump administration’s move would most likely break the law. Anne Joseph O’Connell, an administrative law professor at Stanford University, said that folding the agency into the Commerce Department would violate the Postal Reorganization Act of 1970. Although the Postal Service was once a cabinet-level department, the law converted it into an independent agency run by a board of governors that consists of up to nine governors who are appointed by the president and confirmed by the Senate.

“They would need congressional permission,” Ms. O’Connell said.

Mr. Trump’s plans unnerved union leaders and Democratic lawmakers who have raised concerns about the potential ramifications for millions of Americans across the country who depend on the agency for their mail delivery.

“This shortsighted effort will do nothing to improve delivery performance or set the Postal Service on a path of fiscal sustainability,” House Democrats on the Oversight Committee wrote in a letter on Saturday. “It could instead subject the Postal Service and the entire mail network to political interference, shifting priorities of administrations and skyrocketing prices.”

The Postal Service did not respond to requests for comment.

Efforts to privatize the post office could lead to a deterioration in the quality of service in rural areas, given that private companies would be less incentivized to deliver to those communities, said James S. O’Rourke, a professor of management and organization at the University of Notre Dame who has studied the Postal Service.

“Mr. Trump has talked about Amazon, UPS and FedEx, but they probably don’t want a third of what the U.S. Postal Service delivers,” Mr. O’Rourke said.

The Postal Service’s “universal service obligation” requires the agency to deliver to everyone in the United States at a reasonable price, although the mandate is vaguely defined. The agency delivers to roughly 167 million addresses, covering every state, city and town.

Mr. O’Rourke said he was also concerned about the potential implications for the delivery of mail-in ballots, and whether the Trump administration would continue the service if it controlled the Postal Service.

“I think that’s very worrisome, given how many were delivered in the last election,” Mr. O’Rourke said. “The president in recent years has vigorously criticized vote by mail.”

Some Republican lawmakers have said that major changes are needed to stabilize the agency, and they praised Mr. Trump’s ambitions. “It is no secret that I am a huge critic of the disastrous way the U.S.P.S. has been run,” Representative Rich McCormick, Republican of Georgia, said in a statement. “It’s time for some big changes, and I applaud President Trump for working to solve this problem with outside-the-box solutions.”

In recent months, both Democrats and Republicans have slammed the postmaster general, Louis DeJoy, over what they say is a failed attempt to improve the agency’s finances and service. Last week, Mr. DeJoy announced that he would step down and “start thinking about the next phase of my life” after more than four years in the role.

Mr. DeJoy has been the face of a major 10-year modernization plan that the post office rolled out in early 2021, an effort to shore up an agency that had lost $87 billion over 14 years. The plan, called Delivering for America, included consolidating locations, raising prices and lengthening promised delivery times.

The plan had initially projected that the Postal Service would break even by the 2023 fiscal year. But the agency has continued to lose money, which postal management has attributed to high inflation, increased labor costs and a lack of administrative action that would adjust the agency’s pension costs. Although the agency has received some federal relief in recent years, it generally does not receive tax dollars for operating expenses and instead relies on revenue from its sales.

The Postal Service has also struggled with service declines. In the 2024 fiscal year, 81 percent of single-piece first-class letters and postcards were delivered on time, which reflects the mail category that households use most often. That was down from 88 percent the year before, and below the agency’s target of 92 percent, according to Postal Service data.

Some who closely watch the Postal Service said there were signs that the agency’s finances were improving. They also underscored that its leaders still had several years left to complete the modernization plan, which they said was not intended to immediately fix the agency’s longstanding challenges.

“It’s not all gloom and doom,” said Mark Dimondstein, the president of the American Postal Workers Union, which represents more than 200,000 Postal Service employees and retirees. “If this administration wants to help the finances, there are easy ways to do it besides having a coup.”