Nearly two dozen Democratic senators are calling on Donald Trump to sell his business holdings to avoid conflicts of interest when he becomes president.

The senators sent a letter to Trump's transition office Tuesday -- the day after he postponed a press conference at which he had promised to talk about removing himself from the operations of his business empire.

The letter said Trump's holdings create "the potential for serious conflicts" between the country's interests and his personal financial interests. They said he should sell his business holdings and put the proceeds in a trust controlled by an independent manager.

The 23 senators who signed the letter included Tom Carper of Delaware, the top Democrat on the Senate Homeland Security and Governmental Affairs Committee.

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They join a raft of officials and government ethics experts of both parties who have called on Trump to dump his assets. The president-elect owns or has a position in more than 500 companies around the world, according to a CNN analysis.

Ethics experts have stressed that maintaining an ownership stake in his properties will invite constant questions about whether Trump is acting in the public interest or for his own profit.

Trump had promised to detail a plan for his businesses at a "major news conference" on Thursday. Instead, he said on Twitter that he was rescheduling for January.

I will hold a press conference in the near future to discuss the business, Cabinet picks and all other topics of interest. Busy times! — Donald J. Trump (@realDonaldTrump) December 13, 2016

He did say that his sons Donald Jr. and Eric would manage the business along with "executives." He also said "no new deals will be done during my term(s) in office."

He did not suggest he was ready to sell anything.

"It really doesn't address central, core ethical issues," said Larry Noble, general counsel of the Campaign Legal Center, a nonpartisan, nonprofit government watchdog group. "And unfortunately, I think it reflects a lack of understanding on his part of what a conflict of interest is."

Representative Elijah Cummings, the ranking Democrat on the House Oversight Committee, called the delay "very concerning."

"Mr. Trump cannot even meet his own self-imposed deadline and now appears to be brushing aside these serious problems," he said in a statement.

Norman Eisen, a visiting fellow at the Brookings Institution and former ethics czar for President Barack Obama, has repeatedly called on Trump to fully divest. He called Trump's latest proposal a "half-measure" and "half-truth."

"Complex enterprises like Trump's require constant new negotiations, transactions and terms," Eisen wrote with Richard Painter, a former ethics lawyer for President George W. Bush, in an op-ed published Tuesday in The Washington Post. "So Trump's concept of 'no new deals' is questionable."

Painter and Eisen wrote that Trump's decision to put his sons in charge of the business was also a concern, adding that such moves are "a typical conduit for corruption all over the world."

"If Trump maintains an ownership interest in the businesses, and his kids are running them, that is an invitation for scandal," they wrote.

Related: How Donald Trump might handle conflicts of interest

Kenneth Gross, a former Federal Election Commission lawyer who has provided legal assistance to several presidential campaigns, said he thinks Trump's pledge to form "no new deals" could be a significant, "positive development."

Gross added, however, that the promise would likely not extend to matters involving current business arrangements, like re-upping current deals or renegotiating current loans or leases.

"Otherwise the sons would have to systematically close out properties and existing arrangements as they come due, which I would not expect to happen," Gross said. "In short, I take it to mean the business will be not acquisitive but it won't be in mothballs either."

While details on Trump's business plan are still vague, he could ensure that his sons don't enter into new deals by structuring a binding agreement to that effect, said David Rivkin Jr., an attorney who worked in the Justice Department under Presidents Ronald Reagan and George H.W. Bush.