Chi Phi, One of the Nation's Oldest Fraternities, Votes to Allow Some Transgender Men But, transgender men will need to provide valid legal documentation to join.

 -- One of the nation's oldest fraternities has voted to allow transgender men with legal documentation to pledge -- saying that "one change is never a stopping point" and saying it hopes "this opens the door to further discussion about inclusivity."

Chi Phi, which was founded at Princeton University in 1824, changed its membership policy to be more inclusive following a student-run initiative at its 151st congressional meeting, the fraternity announced last week.

"We felt this amendment to Chi Phi's Constitution would change the conversation surrounding transgender men and their ability to join the Fraternity," said Sam Borchart, the undergraduate chairman of the Committee of Membership. "One change is never a stopping point, and we hope this opens the door to further discussion about inclusivity, particularly for transgender men who want to join us in this fraternity."

The policy change is effective immediately and states eligibility will include any male as defined by legal documentation, the fraternity said. It was not immediately clear exactly what types of documents would qualify. A representative for Chi Phi's national headquarters in Suwanee, Georgia did not immediately respond to ABC News' request for comment.

The National Center for Transgender Equality praised Chi Phi's aim to be more inclusive, but expressed concern regarding its requirement for legal documentation, citing varying state rules about how one qualifies for updated documents.

"All educational programs and facilities, including Greek life, should be open to trans and all students," said Mara Keisling, Executive Director for the National Center for Transgender Equality. "We would caution the fraternity that their use of the “valid legal documentation” as a definition of who may join Chi Phi still will limit many of the people they hope to expand to include."

Each of Chi Phi's 52 individual chapters select their own members. The fraternity's motto is "Building Better Men," according to its website.

Chi Phi is not the first Greek organization to promote inclusivity in its member policy. Six years ago, Zeta Chi at Trinity University in San Antonio allowed a transgender woman to rush the sorority, according to a Thinkprogress.org piece titled "Greek Organizations Are Slowly Becoming More Trans Inclusive."

Last fall, Missouri State's Xi Omicron Iota changed its bylaws to accept anyone who "identifies as a girl, while in August, national fraternity Sigma Phi Epsilon voted to welcome any individual who identifies as a man to seek membership, according to Thinkprogress.org, The University of Texas' Gamma Rho Lambda because the first LGBT-inclusive sorority in March 2015.

The National Multicultural Greek Council is unable to order individual fraternity and sorority organizations on how to consider transgender students, it told ABC News.