The Trump Foundation, a charitable organization that Republican presidential nominee Donald J. Trump has used in the last year to solicit donations, has been operating illegally without proper Charities Bureau registration, according to New York Attorney General Eric T. Schneiderman's office.

Trump's campaign has agreed to immediately stop soliciting donations in New York State, following its receipt of a cease-and-desist letter from Schneiderman's office, mailed Friday and made public Monday morning.

The foundation “is in violation of section 172 of Article 7-A New York's Executive Law, which requires charitable organizations that solicit contributions in New York State to register with the Charities Bureau and to provide annual financial reports and annual audited financial statements," according to the AG's office.

Under New York State law, charities that take in more than $25,000 per year from the public must complete such a registration. Tax filings reviewed by the Washington Post show that the Trump Foundation raised more than $25,000 from the public in each of the last ten years.

The outlet noted that it's not possible to determine from public documents whether all of these donations where solicitations under state law, adding that the technical definition of "solicitation" is broad. "The only thing it wouldn’t cover is somebody giving money without being asked,” Pamela Mann, a former head of the New York State charities bureau, told the Post.

Some of the solicitations may have been made outside of New York, and would not, therefore, be in violation of state law.

Reporters have been probing Trump's charitable donations—or lack thereof—for months, and skepticism about the Trump Foundation has been building. The NY Times recently reported that the Trump Foundation doesn't show up on charity registers in multiple states, and the Washington Post reported that the foundation had not acquired proper certification in New York, one day before Schneiderman announced his investigation.

The notice from Schneiderman's office [PDF] orders the Trump Foundation to "immediately cease soliciting contributions or engaging in other fundraising activities in New York," and to hand over all of the paperwork required as part of a typical Charities Bureau application, including annual financial reports and audited financial statements, according to the NY Times.

The Washington Post points out that the application is intended, in part, to make sure that the foundation doesn't spend any of its money "for the personal benefit of its officers."

"While we remain very concerned about the political motives behind A.G. Schneiderman’s investigation, the Trump Foundation nevertheless intends to cooperate fully with the investigation," Trump spokeswoman Hope Hicks stated on Monday. "Because this is an ongoing legal matter, the Trump Foundation will not comment further at this time."

Schneiderman could reportedly seek court permission to demand that Trump return all of the money his organization has raised in New York, depending on the investigation's outcome.