The outgoing head of the Office for Government Ethics has a message for President Trump: Don't visit your own properties while you're in office.

Walter Shaub, who announced that he's leaving the federal government earlier this month, told CNNMoney on Monday that it's something he's relayed to the Trump team before.

"[I had] some very specific recommendations, like stop going to your properties or announce that White House officials won't go to those properties," Shaub said.

Those visits amount to free promotion, Shaub said.

"You've got the president traveling there every single weekend, and whether he intends to or not, he's giving free advertising to them," he said.

This past weekend, Trump visited Trump National, his private golf club in Bedminster, New Jersey, to attend the U.S. Women's Open.

He's now spent 40 days of his presidency at a Trump golf property. Of the 26 weekends he's been in office, Trump has spent 21 weekends at a property that bears his name.

Related: Top golfers, Trump and protesters come out for U.S. Women's Open

The White House, in a statement, denied that Shaub had brought his concerns to them directly.

"Mr. Shaub has been outspoken by leaking, tweeting, and writing letters to Democrat members of Congress, but since the president was sworn into office, he never once raised travel, passive holdings or other ethics issues involving the president in a single discussion with the White House counsel or deputy counsel overseeing ethics and compliance," the White House said.

Related: Trump's 17 golf courses: Everything you need to know

Shaub's resignation is effective on Wednesday. He's moving to the Campaign Legal Center, a nonprofit, nonpartisan advocacy group for tougher campaign finance laws.

"I resigned because I've achieved all I can in this job in the current circumstances," Shaub told CNNMoney.

Shaub has clashed repeatedly with the Trump White House.

In January, he lambasted the president's decision to not sell his business holdings. In March, he criticized the White House's decision not to punish Kellyanne Conway after she plugged Ivanka Trump's products in a TV interview. And in May, Shaub tussled with the White House over the release of ethics waivers that were granted to staffers.

Related: Ethics official who sparred with Trump is leaving government

Trump's unwillingness to part with his business empire remains a major point of contention for Shaub.

"You've seen foreign governments schedule events at his hotel and we don't know if they would be doing that otherwise," Shaub said. "There have been fundraisers there, charity events, politicians holding events at his properties. ... These are the kinds of things that should worry us."

It also makes it difficult to parse the president's motivations, he said.

"You see him holding financial interests -- that leaves us unable to know whether decisions are motivated by policy aims or by personal financial interests," Shaub said.

Shaub said the executive branch under Trump has retreated from established norms on government ethics, he said.

"We are in a state of crisis right now," Shaub said. "I'm very concerned about the risk to the integrity of government."

-- CNN's Dan Merica and Steve Brusk contributed to this report.