Representatives Fred Upton, the chairman of the House Committee on Energy and Commerce, and Cliff Stearns formally asked EPA Administrator Lisa Jackson on Thursday if she used an account with the alias "Richard Windsor" and whether she has used any other accounts assigned by the agency.
Lawmakers and a public interest watchdog group have complained that Jackson's second account - named after a family dog - was not something that could be easily linked to the administrator.
Emails Jackson wrote using that account may not have been captured by Freedom of Information Act requests or made it to national archives, they argued.
"We recognize the utility of a secondary, internal email account for the conduct of agency business," the lawmakers said in a letter to Jackson. "We seek to understand whether conducting business with an alias has in any way affected the transparency of the agency's activities."
Upton's committee has for two years been seeking information and documents related to EPA decisions on pollution rules, but his chamber has not been able to slow or halt the regulations.
The email alias was first revealed last month in articles by climate-change skeptic Chris Horner, of the American Tradition Institute, who discovered it while doing research for a book.
EPA administrators have been assigned two email accounts - for public and internal use - for more than a decade, the agency said in a statement in November.
On Thursday the EPA said "responsive records" for both Jackson's public and internal accounts are provided to FOIA requesters.
Last month, a non-partisan government watchdog group asked the EPA's inspector general to investigate the fake account.
"The easy fix would be to have an account that is more identifiable as the administrator's," said Anne Weismann, the chief counsel for Citizens for Responsibility and Ethics in Washington. The arcane alias made the potential for abuse that much higher, she said.
The lawmakers also asked the EPA to tell them within a week whether Jackson used an alias for communications with all EPA employees or a select group and whether she had used an alias with any non-governmental third parties.
(Reporting by Timothy Gardner; Editing by Tim Dobbyn and Gunna Dickson)