A Washington attorney suing the Obama administration for access to alias emails sent by EPA Administrator Lisa Jackson claims that a recent decision by the Justice Department to release thousands of those emails next month contributed to her resigning Thursday.
Jackson, in a brief written statement, said Thursday she is leaving the EPA after four years on the job, for "new challenges, time with my family and new opportunities to make a difference."
The agency did not offer an explanation. But Chris Horner, a senior fellow at the Competitive Enterprise Institute, said the scrutiny over the alias emails is clearly a factor.
"Life's full of coincidences, but this is too many," he told FoxNews.com. "She had no choice."
Horner and CEI earlier this year had sued the EPA for documents pertaining to Jackson's use of alias email accounts. She was said to operate under the name "Richard Windsor" -- the use of those accounts has since drawn the scrutiny of Republican members of Congress, as well as triggered an audit by the EPA inspector general.
According to court documents, the EPA -- represented by the Justice Department -- two weeks ago agreed to release as many as 12,000 emails pertaining to the CEI request beginning by Jan. 14, at a rate of 3,000 documents per month. The court accepted the schedule last week.
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Horner said the increased scrutiny on the alias account, coupled with what those emails might contain regarding the administration's alleged "war on coal," likely contributed to Jackson's announcement Thursday.
"She, by her action, told us that these are records she doesn't want the people to see," Horner said.
President Obama, in a written statement, made no reference to the emails.
"Over the last four years, Lisa Jackson has shown an unwavering commitment to the health of our families and our children," Obama said. "Under her leadership, the EPA has taken sensible and important steps to protect the air we breathe and the water we drink ... I wish her all the best wherever her future takes her."
Asked for a comment Thursday, an EPA representative referred FoxNews.com back to Jackson's earlier statement.
In November, when reports of the alias accounts were first surfacing, an EPA spokesman said the agency has for roughly a decade assigned internal and public email addresses to administrators -- and that they use the internal ones to communicate with staff because of the massive amount of traffic on the public accounts.
The spokesman also said both accounts are reviewed and made available when a Freedom of Information Act request is made.
Republican lawmakers, though, expressed concern about the accounts, and particularly the use of a fake name.
"While we understand the need for a secondary account for management and communications purposes, your choice to use a false identify remains baffling," Republicans on the House Committee on Science, Space and Technology wrote to Jackson last week.
Earlier in the month, the EPA inspector general's office confirmed that it was opening an audit into the agency's "electronic records management practices." The office said they would look into whether the EPA was, among other things, encouraging the use of "private or alias email accounts to conduct official government business."
Horner has said the agency's use of secret email accounts dates back to the Clinton administration and then-Administrator Carol Browner. He called Jackson's account a "deliberate, several stage deception."
Jackson's tenure was marked by a string of high-profile fights between her agency, and the energy industry along with congressional Republicans. Goals for a cap-and-trade climate bill in Congress were scuttled early on in the Obama administration, but her agency went on to set new fuel efficiency standards for U.S. vehicles, as well as new rules for power plants.
She played a role in pushing for a delay in the Canada-to-Texas Keystone XL pipeline. All along, Republicans in Congress repeatedly tried to block EPA regulations on coal and other industries.
Fox News' Doug McKelway contributed to this report.