The New York attorney general has accused Secretary of State Rex Tillerson of using the pseudonym "Wayne Tracker" to send emails related to climate change while serving as CEO of Exxon Mobil.

The office of Eric Schneiderman revealed the unorthodox arrangement in a letter sent to a New York state judge on Monday that also accused Exxon of failing to produce documents related to an investigation into whether the company misled investors over climate change.

Schneiderman's office said that Tillerson used the "Wayne Tracker" alias from at least 2008 to 2015. They said it was used to "send and receive materials regarding important matters" including climate change.

"Despite the company's incidental production of approximately 60 documents bearing the "Wayne Tracker" email address, neither Exxon nor its counsel have ever disclosed that this separate email account was a vehicle for Mr. Tillerson's relevant communications at Exxon," Senior Enforcement Counsel John Oleske wrote in the letter.

Tillerson's middle name is Wayne.

The State Department said that inquiries related to Tillerson's email accounts should be directed to Exxon (XOM).

The oil company confirmed that Tillerson had used the "Wayne Tracker" email while CEO. In a statement it also said it had provided more than 2.5 million pages of documents to the attorney general.

"The email address, Wayne.Tracker@exxonmobil.com, is part of the company's email system and was put in place for secure and expedited communications between select senior company officials and the former chairman for a broad range of business-related topics," spokesman Alan T. Jeffers said in statement.

Tillerson has significant sway over climate change issues as secretary of state. He could, for example, negotiate a U.S. exit from the Paris climate agreement. During confirmation hearings, the former oil man refused to answer questions about whether Exxon had ever downplayed or obscured climate research.

He is far from being a climate change denier, however. With Tillerson as CEO, Exxon acknowledged in 2006 that climate change is a problem. The company later endorsed a carbon tax and backed the Paris climate agreement.

Related: Tillerson ducks Exxon climate change allegations

Schneiderman's office said the discovery of Tillerson's second email address lends "additional urgency" to their demand that Exxon turn over documents related to climate change.

A wider problem?

In addition to the email alias used by Tillerson, Schneiderman's office said that it has identified 34 other email accounts assigned to top executives, board members and their assistants that had not been disclosed by Exxon.

Related: Will Rex Tillerson get a tax break on his big Exxon payout?

Schneiderman's office requested that the court order Exxon to produce documents related to the accounts.

"Exxon's top executives, and in particular, Mr. Tillerson, have made multiple representations that are at the center of [our] investigation of potentially false or misleading statements to investors and the public in regard to these purported internal safeguards," they wrote.