The lawsuit was filed last month by Delta Lambda Phi in federal court in Eugene, Ore.
It claims that Delta Lambda Psi, which started at the University of California at Santa Cruz in 2005, has caused confusion with the public and on Twitter and MySpace by deliberately choosing a name that differs by one Greek letter and also using the same abbreviated designation of DLP. There is another Delta Lambda Psi chapter at Northeastern Illinois University.
Delta Lambda Psi has shown it intends to expand the infringement of Delta Lambda Phi's trademark by opening a third chapter at the University of Oregon in Eugene, Ore., the lawsuit said.
The lawsuit asks a judge to order Delta Lambda Psi to change its name and pay damages.
Delta Lambda Psi spokesman D.J. Bott said in an email Friday that his gender-neutral organization, which accepts men and women of all sexual orientations, is not competing with the fraternity for gay men.
"We have tried to address Delta Lambda Phi's concerns," expressed in a letter in July, he wrote. But instead, the other fraternity went to court.
He added his organization is not affiliated with the Delta Lambda Psi at the University of Oregon.
Delta Lambda Phi was founded in 1986 to promote the interests of gay, bisexual, transgender and progressive students, the lawsuit said. It has 30 chapters and four colonies across the U.S. and Canada with 400 undergraduate members and 2,500 alumni.
"Delta Lambda Psi's opening of a new chapter at the University of Oregon in Eugene has made the need to address this harm particularly urgent," Delta Lambda Phi attorney John Mansfield wrote in an email. "DLP offered several times to meet with Delta Lambda Psi face-to-face to resolve the dispute in person, but Delta Lambda Psi never responded to any of those offers."