An e-mailer who has been sued by the developer Bruce Ratner is fighting in court to preserve his anonymity.

Nearly two months ago, Mr. Ratner filed a federal lawsuit against an emailer who pretended to be Mr. Ratner in an e-mail regarding the Atlantic Yards Development Project. The lawsuit claimed the message was intended to undermine public support for Mr. Ratner’s project, which has drawn opposition from some residents near downtown Brooklyn.

Mr. Ratner’s attorneys have subpoenaed the Internet service provider Earthlink, demanding that it identify the person who sent the e-mail.

In papers filed last month in federal court in Atlanta, where Earthlink’s legal division operates, a lawyer for the e-mailer opposed the subpoena.

The lawyer, Mark Bierman said the lawsuit was an attack on his anonymous client’s First Amendment rights. In court filings, Mr. Bierman accused Mr. Ratner of “using this lawsuit as a weapon to stifle opposition to his mega development project.”

The e-mail that prompted the dispute was addressed to the president of Brooklyn Brewery, Stephen Hindy, who is a public supporter of Mr. Ratner’s project. The message was meant to look like it came from Mr. Ratner’s e-mail account. The phony e-mail stated that Mr. Hindy would not receive a contract to sell beer in the basketball arena that Mr. Ratner intends to build as part of the project.

Mr. Bierman claims that his client has a right to remain anonymous. In the court filing, he characterized the e-mail as “tongue in cheek” and “satirical.”

Lawyers for both Mr. Ratner and the e-mailer are scheduled to appear in federal court in Brooklyn for the first time on June 5.