House investigators pressed outgoing Environmental Protection Agency (EPA) Administrator Lisa Jackson, in a letter noting criminal penalties for hiding federal records, to reveal all of the email accounts that she and agency employees use to conduct official business.

Jackson is receiving the letter just days after the EPA had to release, because of court order, 2,100 emails associated with an email account registered in the name of “Richard Windsor,” which was actually an alias used by Jackson.

Related: Glitches mar EPA release of first batch of ‘Windsorgate’ emails

“The use of an alias account to conduct official Agency business makes compliance with the [Federal Records Act] and [Presidential Records Act] more difficult because the alias may not be matched to an actual Agency employe,” House Oversight and Government Reform Committee chairman Darrell Issa, R-Calif., wrote in the Wednesday letter, which was obtained exclusively by The Washington Examiner.

“The use of an alias email account to conduct government business also creates difficulties in fulfilling the FOIA or litigation requests. Furthermore, conducting official business using an alias may implicate criminal or civil penalties for the unlawful concealment of federal records,” Issa added. The committee asked for a response by January 29th.

The House Energy and Commerce Committee has also written the agency about the secret email account, while the EPA inspector general has begun an investigation.

“Our objective is to determine whether EPA follows applicable laws and regulations when using private and alias email accounts to conduct official business,” assistant inspector general Melissa Heist wrote to the EPA on December 13, 2012.

Jackson said that she used the “Richard Windsor” account as a secondary account due to the large amount of email that her primary official account receives. The use of a secondary email is common enough, but some observers have criticized the lack of transparency associated with this account.

“I don’t know any other agency that does this,”  Anne Weismann of the Citizens for Responsibility and Ethics in Washington told Politico. “[W]hy would you pick a fictitious name of someone of different gender? To me it smacks of … trying to hide.”

Chris Horner of the Competitive Enterprise Institute, which filed the lawsuit that led to the release of the Richard Windsor emails, criticized the EPA after receiving the first tranche of messages on Monday.

“Perhaps seeking to take the air out of a growing scandal, EPA’s defective compilation boasts an impressively anemic content-to-volume ratio,” Horner told CNS News. “It starts with Washington Post daily news briefs, then follows with Google alerts for “Lisa Jackson EPA” (none for “Richard Windsor”). Then EPA HQ national news clips. And so on. Rope a dope. Clever. Maybe too much so.”

The EPA has promised to release more emails. Sen. David Vitter, R-La., suggested that the agency do so without redacting the name associated with the account from the email address, as they did with the first batch.

“The EPA needs to honor the President’s pledge of transparency and release these documents without redaction of the Administrator’s email address – a big first step toward removing the blanket of secrecy in this agency,” Vitter, the top Republican on the Senate Committee on the Environment and Public Works, said in a statement on Wednesday.