The public entrance to Trump Tower on Fifth Avenue in New York.

New York state regulators have issued a subpoena to the insurance brokerage Aon for President Donald Trump's company as part of a large probe into the Trump Organization's business practices.

The nine-page subpoena to Aon was issued by the New York Department of Financial Services late Monday evening, according to a source familiar with the case, who spoke to CNBC on the condition of anonymity.

The demand for documents came five days after Trump's former personal lawyer Michael Cohen told the House Oversight and Government Reform Committee that Trump himself had inflated company assets for insurance purposes.

"We can confirm that we received a subpoena from the New York State Department of Financial Services and, as is our policy, we intend to cooperate with all regulatory bodies," Aon said in a statement.

"We do not comment on specific client matters."

The DFS probe is a civil investigation. However, any evidence of criminal activity discovered by the department can be referred to state prosecutors.