Treasury Secretary Steven Mnuchin addressed a group of top donors backing President Trump’s reelection Tuesday evening, making an unusual political appearance at a gathering that included industry executives his agency is tasked with regulating.

Mnuchin’s attendance at the kickoff event for the Trump Victory Committee came a day after he rejected a request from House Democrats for Trump’s tax returns and as the Dow Jones industrial average fell sharply amid a trade standoff between the United States and China.

Mnuchin was not listed as an official speaker at the event, held at the Trump International Hotel in Washington, according to a copy of the agenda obtained by The Washington Post.

But Tim Murtaugh, a spokesman for the reelection committee, confirmed that the Trump campaign invited Mnuchin to deliver brief remarks. He said participants came from “a wide range of American industries, including the financial sector.”

Among those who were invited was Trump friend and billionaire Stephen Schwarzman, chief executive of the private equity giant Blackstone Group, who did not attend, according to a person familiar with the invitation.

Treasury secretaries in recent years have avoided attending fundraiser events with people they could be tasked with regulating, in part because of their unique role in overseeing a broad swath of companies in the financial system.

“There’s a legitimate concern that people may get the impression that they can get not just on Trump’s good side but the treasury secretary’s good side by donating or raising money for his campaign,” said Kathleen Clark, a legal and government ethics professor at Washington University School of Law.

Cabinet secretaries can appear at campaign events as private citizens without violating the Hatch Act, a federal law that prohibits public employees from using their official capacity to conduct political activity. But the law prohibits them from being named by their official title in connection with their appearance, either in introductory comments or official event materials, and from soliciting donations.

Treasury Department officials said Mnuchin planned to attend the event in his personal capacity and that he first sought guidance from Treasury’s ethics officials.

Mnuchin did not solicit or accept any donations at the event, “nor is he utilizing Treasury resources” at the gathering, according to a Treasury spokeswoman.

Murtaugh said that Mnuchin was not going to be introduced with his official Cabinet title and would not take questions.

“Throughout the course of all administrations, Cabinet secretaries have engaged in political events . . . in their own time,” Murtaugh said. “The campaign and the administration know the rules, and appropriate precautions will be made to make sure that his participation is appropriate and permissible.”

The Tuesday afternoon event for the president’s reelection campaign drew about 200 people, known as “bundlers,” who are raising money and collecting checks for the president’s campaign and the Republican National Committee.

Since Mnuchin was scheduled to appear in a personal capacity, his name was left off the official agenda, the Trump campaign said.

However, among the speakers listed in the program was senior White House adviser Kellyanne Conway, who was set to do a ­question-and-answer session with campaign spokeswoman Kayleigh McEnany.

Conway was identified only with the title of “Honorable.” She appeared as a “special guest for this event” and “her participation is not a solicitation of funds,” according to a disclaimer at the bottom of the agenda.

Mnuchin spoke right before Vice President Pence, who closed out a reception at the end of the day, according to two attendees. He spoke briefly and did not mention his title, one said.

Restrictions under the Hatch Act do not apply to the vice president or the president.

Among the fundraisers in attendance were oil magnate Harry Sargeant III; Thad Beshears, an executive of Florida-based Simpson Nurseries; and lobbyist Brian Ballard, according to an attendee who spoke on the condition of anonymity to share participant information.

They listened to presentations by top officials from the Trump campaign and the RNC, including RNC Chairwoman Ronna McDaniel, Trump Victory Committee national finance chairman Todd Ricketts, Trump campaign manager Brad Parscale and Kimberly Guilfoyle, senior adviser to the campaign and a former Fox News host, the agenda shows.

Mnuchin’s scheduled attendance on Tuesday came a day after he told Democrats he would not furnish six years of Trump’s tax returns, even though a number of legal experts said Mnuchin should have been obligated to supply the records under a 1924 law.

Mnuchin — who served as national finance chairman of Trump’s 2016 campaign — had been one of his closest advisers in the first 18 months of the presidency. Trump soured on him late last year because the stock market started sinking. Trump also blamed Mnuchin for advising him to appoint Jerome H. Powell as Federal Reserve chairman, a decision the president has told confidants he regrets.

As treasury secretary, Mnuchin could not use any department resources in connection with his appearance, such as asking an agency speechwriter to write his remarks. He also could not speak to specific Treasury policies or the Trump administration’s policies, or discuss any policy items the administration may address during a potential second term, according to Hatch Act experts.

However, he could broadly address about the president’s record affecting the financial industry or the state of the economy, or his support of the Trump presidency, experts said.

His presence would be acutely noted by industry executives in attendance, said legal experts, who noted that the 2010 Dodd-Frank financial regulation law gave Mnuchin tremendous power over a broad swath of companies.

That law made the treasury secretary the chairman of the Financial Stability Oversight Council, a group of regulators that is tasked with looking across the financial system to intervene when necessary to prevent dangerous behavior.

“The feeling would be that he would have the ability to remember who was helpful and who was not helpful,” said Arthur Wilmarth, a professor at George Washington University Law School.

“He now has direct regulatory power both as chairman of FSOC and the primo voting member of FSOC, certain things can’t happen without his vote,” Wilmarth said.

Previous Cabinet secretaries have drawn fire — and occasionally legal reprimands — when they have gotten involved in political events.

In 1996, a firestorm erupted when President Bill Clinton, Treasury Secretary Robert Rubin and a top bank regulator attended a “coffee” fundraiser with top bankers at the White House. Republicans slammed the event, saying it posed a conflict of interest.

Clinton later denied having made any decisions based on fundraisers but did say the optics of the event were poor and that “mistakes were made.”

Housing and Urban Development Secretary Ben Carson spoke at a Trump rally in 2017 in his personal capacity, but was introduced with his official title, prompting a complaint alleging he violated the Hatch Act.

The Office of Special Counsel dismissed the complaint, saying the person who introduced Carson with his official title was not authorized to do so, and that Carson “did not hear his introduction before he spoke at the rally.”

President Barack Obama’s secretary of housing and urban development, Julián Castro, violated the Hatch Act when he answered a question about the presidential race during a television interview.

Castro had claimed he was answering the question as a private citizen, but the Office of Special Counsel found he still violated the law because he was appearing in the interview as a HUD official.

For his part, Trump has privately dismissed concerns about the Hatch Act, sympathizing with aides found to have violated it, according to current and former White House officials.