Cohen is known to have paid porn star Stormy Daniels $130,000 on the eve of the 2016 presidential election in exchange for her silence about an alleged affair with Trump.
Earlier this month, one of Trump's new lawyers, Rudy Giuliani, confirmed for the first time that the president reimbursed Cohen for that payment.
In recent days, a looming question was whether Trump's financial disclosure form would mention Cohen's payment to Daniels and Trump's reimbursement for it, as a leading government ethics expert said it must.
The federal Office of Government Ethics, in a letter to the Justice Department released Wednesday, said that "the payment by Mr. Cohen" to a third party by law should have been revealed in Trump's financial disclosure filing last year.
However, the payment was not revealed in that filing. The OGE's acting director on Wednesday gave the Justice Department both this year's report and last year's report "because you may find the disclosure relevant to any inquiry you may be pursuing."
Former OGE Director Walter Shaub said that the acting director's letter to the Justice Department is "tantamount to a criminal referral."
The disclosure filed Wednesday does not mention the reason Trump paid Cohen for the payment the lawyer made.
But it says that Cohen incurred expenses in 2016 and that he sought reimbursement for those expenses, "and Mr. Trump fully reimbursed Mr. Cohen in 2017."
The "category of value" of the reimbursement Trump paid Cohen according to the disclosure is not a specific amount, but a range: $100,001 to $250,000.
The disclosure also says, in a footnote, that the expense claimed by Cohen was "not required to be disclosed as 'reportable liabilities'" on the form. But the expense was being revealed, according to the disclosure, "in the interest of transparency."
But the Office of Government Ethics, in a letter to Deputy Attorney General Rod Rosenstein, said that the payment made by Cohen "is required to be reported as a liability."
The OGE's acting director, David Apol, noted that the interest group Citizens for Responsibility and Ethics in Washington in March had filed a complaint with both the Justice Department and OGE.
That complaint asked both agencies to investigate whether Cohen's payment to Daniels "constituted a loan to President Trump that should have been reported as a liability on his public financial disclosure report signed on June 14, 2017." That report covered calendar year 2016, the same year that Cohen paid Daniels.
CREW also asked both agencies to determine if the failure to disclose such a loan "was knowing and willful."
Apol wrote Rosenstein that OGE "has determined that the information" detailing the payment by Cohen and the reimbursement by Trump "meets the disclosure requirements for a reportable liability under the Ethics in Government Act."
Apol wrote that he was giving "both reports" to Rosenstein "because you may find the disclosure relevant to any inquiry you may be pursuing regarding the President's prior report that was signed on June 14, 2017."
On May 4, Democratic Rep. Elijah Cummings said Trump may have broken the law by not disclosing his debt to Cohen in his financial disclosure report last year.
Giuliani's statement in early May that Trump had reimbursed Cohen for the Daniels payment came after Cohen's own lawyer had denied Trump reimbursed Cohen.
Giuliani told the New York Times that Trump paid Cohen in monthly installments of $35,000 beginning after the election, which totaled up to $470,000.
Trump had previously denied knowledge of Cohen's payment to Daniels.
But the president acknowledged the hush money deal and Cohen's reimbursement in a trio of tweets after Giuliani's initial revelations.
Cohen, he said, "received a monthly retainer, not from the campaign and having nothing to do with the campaign, from which he entered into, through reimbursement, a private contract between two parties, known as a non-disclosure agreement."
Trump added that such deals are "very common among celebrities and people of wealth," and that it was used in this case to "stop the false and extortionist accusations made by her about an affair."
Thousands of executive branch employees filed the annual forms on Tuesday — including the president, according to the Office of Government Ethics. Trump's previous filing from June 2017 accounted for nearly $600 million in income — but made no mention of any payments to Cohen or Essential Consultants, the company that Cohen set up to funnel the hush money to Daniels.