Senate Democrats are pushing for more information about business deals between President Donald Trump’s former personal attorney Michael Cohen and two companies that paid him consulting fees, ABC News has learned.

On Friday, a small group of senators sent letters, copies of which can be read below, to Columbus Nova CEO Andrew Intrater and Korea Aerospace Industries CEO Kim Jo-won, whose companies collectively paid Cohen more than half a million dollars in consulting fees following Trump’s election. That money was channeled into Essential Consultants LLC, the same shell company used to make hush payments to adult-film actress Stormy Daniels to stay silent about her alleged affair with the president.

Sens. Elizabeth Warren of Massachusetts, Ron Wyden of Oregon, Richard Blumenthal of Connecticut and Patty Murray of Washington peppered the pair of executives with questions that appear aimed at exploring what made Cohen so valuable to companies engaged in businesses where Cohen’s expertise would appear to be limited.

“Explain Columbus Nova's decision to consider hiring Mr. Cohen,” wrote the senators to the CEO of the New York-based investment firm Columbus Nova, which paid Cohen more than $500,000 in 2017. “What specific skills or knowledge did he bring to Columbus Nova?”

“Explain KAI's decision to consider hiring Essential Consultants and the determination that Mr. Cohen was qualified to advise on "reorganization of ...KAI's internal accounting system, ... Cost Accounting Standards (CAS) and other accounting standards?" Wrote the senators to the CEO of South Korean aerospace company Korea Aerospace Industries, which paid Cohen $150,000 in 2017.

A spokesman for Columbus Nova did not respond to questions from ABC News, but in a statement released in May, the company said “the firm hired Michael Cohen as a business consultant regarding potential sources of capital and potential investments in real estate and other ventures.”

A spokesperson for KAI could not be reached on Thursday, but in May, Oh Sung-keun, a deputy senior manager for KAI, told the Washington Post the company “received legal counseling service from Essential Consultants LLC to inform reorganization of our (KAI’s) internal accounting system,” and suggested that the company did not know about Cohen’s past work for Trump. Oh told the newspaper that the company was “somewhat perplexed by these alleged connections that surfaced recently.”

In May, Stormy Daniels’ attorney Michael Avenatti released what he said were bank transactions showing more than $4.4 million in payments from a number of companies, some foreign and some domestic, to Essential Consultants LLC., a corporation Cohen set up shortly before Election Day.

In some cases, these clients, including Swiss healthcare giant Novartis and telecommunications conglomerate AT&T, had significant business interests in Washington.

Following Avenatti’s release of information, Novartis and AT&T each revealed that the companies had been contacted by Special Counsel Robert Mueller’s office in late 2017 about their respective arrangements with Cohen. Both companies said they cooperated fully and consider the matters closed, but that hasn’t stopped Avenatti.

“Each company has given a different reason for retaining Michael Cohen,” Avenatti told ABC News’s George Stephanopoulos on Good Morning America. “Real estate, business consulting, health care consulting, the list goes on and on.”

In a report released earlier this month, Senate Democrats blasted Cohen for “selling access” to the White House amid questions about whether Cohen’s work could have violated lobbying regulations.

Lanny Davis, an attorney for Cohen, disputed the conclusions drawn by those Senate Democrats, saying that Cohen “did not 'sell access’” but merely “provided strategic advice” to his clients.

ABC News’ Ali Dukakis contributed to this report.