WASHINGTON (Reuters) - Testing the limits of presidential power, Donald Trump this week tightened his grip on U.S. government agencies that for years have taken pride in their independence overseeing such matters as elections, stock markets and labor unrest.

Trump's order on Tuesday was the latest show of force in a series that has removed critics from office, defunded federal programs, loosened government oversight and frozen billions of dollars in spending approved by Congress.

The order allows the White House to shift the budget and policies of the Federal Election Commission, the Securities and Exchange Commission, the National Labor Relations Board and other agencies whose day-to-day activities are traditionally kept at arm's length from the president.

The White House said such oversight provided accountability. Trump has been outspoken in his opposition to what he sees as burdensome regulations, saying they are killing jobs and curtailing Americans' freedom.

Critics called the order another unprecedented power grab, while legal scholars said it would likely be challenged for overstepping the president's constitutional authority.

"What Trump has done is try to push through what are fairly accepted boundaries on presidential authority," said Justin Crowe, a Williams College political science professor.

"Trump's conception of power is one in which the president should be able to do whatever he wants and control whomever he wants. That's how he thinks government should work."

Congress and presidents have traditionally supported the independence of these agencies, believing they needed to be insulated from political pressures to carry out their missions. But many of Trump's fellow Republicans see them as unaccountable and overly stringent on the companies and people they oversee.

Trump has flexed his presidential muscle on issues big and small since taking office on January 20, saying voters gave him a mandate to pursue sweeping changes. He has fired and sidelined hundreds of civil servants and top officials at agencies, installed himself as chairman of the John F. Kennedy Center for the Performing Arts and called for a return to plastic straws.

In a social media post on Wednesday, Trump embraced the notion of a powerful monarch, writing "LONG LIVE THE KING!" with respect to his administration's decision to rescind federal approval of New York City's traffic congestion pricing program.

Official White House social media accounts posted a fake magazine cover showing Trump wearing a crown. 

On Wednesday night aboard Air Force One, he threw his support behind calls for the federal government to take over the U.S. capital city of Washington, D.C. He also signed an executive order instructing the heads of every agency to undertake a review of all regulations, working with members of billionaire Elon Musk's Department of Government Efficiency.

Americans are divided over Trump's steps on executive power, according to a Reuters/Ipsos poll conducted in the past week.

Some 63% of Republicans think the country is in crisis and needs a president who rules without much interference from courts and Congress, the poll found, while 52% of Americans overall disagree.

'POWER GRAB'

The Trump order on Tuesday required the defective-product recall overseers at the Consumer Product Safety Commission, the bank insurers at the Federal Deposit Insurance Corporation and the power regulators at the Federal Energy Regulatory Commission to run any substantive policy changes by the White House. 

Each must install a political appointee on its staff who consults with the White House.

The order bars executive branch employees from expressing legal opinions at odds with the president as the official view of the government. The White House says this will prevent a range of agencies offering conflicting legal interpretations.

"For the Federal Government to be truly accountable to the American people, officials who wield vast executive power must be supervised and controlled by the people's elected President," said the order, which refers to the regulatory agencies as "so-called" independent. 

Critics accused Trump of overstepping executive authority. 

"This is a dangerous power grab by an unhinged president willing to put Americans' lives and livelihoods at risk to consolidate his own control," said U.S. Representative Frank Pallone, a New Jersey Democrat.

"We are not subservient to a king or anyone else out of Washington," New York Governor Kathy Hochul said.

The White House did not respond to a request for comment.

The executive order gives the president new leverage to intervene in a sector of the government that holds vast powers over industries from finance to energy, the internet and consumer products, and that has on occasion angered the corporations it polices.

Trump's effort tests a legal precedent set in a 1935 U.S. Supreme Court case, Humphrey's Executor v. United States, which upheld the ability of Congress to create agencies with more independence from the White House, according to legal scholars.

"It (Trump's effort) basically overrides congressionally enacted statutes and gives the president power to do what he wants," Bill Baer, an official at the Federal Trade Commission during the Clinton administration, said of Trump's order.

The FTC is among the agencies whose independence is challenged by Trump's move.

Its actions on consumer protection and antitrust actions drew corporate ire during the Biden administration, and the agency is pursuing cases accusing both Amazon.com Inc and Facebook owner Meta Platforms of maintaining illegal monopolies.

Amazon executive chairman Jeff Bezos and Meta CEO Mark Zuckerberg both attended Trump's inauguration and have sought to gain favor with the president.

"The concern is that this president, who has been shown to favor those people who are supportive of him, is basically accumulating additional power to reward friends and disfavor enemies," Baer said.

LEAVING THE FED ALONE

Trump's order does not challenge the independence of the Federal Reserve's control over monetary policy. The order's reach is limited to the Fed's financial regulations.

Trump has occasionally threatened the Fed's longstanding independence and pushed it to lower interest rates, but he has avoided a direct clash on the issue.

Analysts said the order could nonetheless result in much more dramatic swings in financial regulation as future presidents exert additional control over bank oversight.

Beyond the impact on individual industries, Mitchel Sollenberger, a professor of political science at the University of Michigan-Dearborn, said the U.S. is seeing a smashing of presidential norms.

"It's a much more sophisticated Trump presidency than the first term," said Sollenberger, author of a book on the "unitary executive" theory, a conservative legal theory that argues the president enjoys sole authority over the federal government's executive branch.

"And I think in many regards, this is a much more aggressive and sophisticated presidency in terms of pushing presidential interest than any presidential administration," he added.