In the past, when deciding about a visa petition based on marriage, the immigration services always looked at the marriage and its validity, following the requirements as outlined in the INA (Immigration & Nationality Act).
That all changed in 2003 under George W. Bush when the government issued a new policy on March 20 regarding marriages with a transsexual spouse. This new policy invalidated all legal marriages between two persons BORN of the same sex.
Little did they know that there are transsexual men and women who are gay/lesbian who now, based on this new policy, would be able to sponsor their same-sex partner for a green card!
This was obviously not what the Bush government intended. On April 16, 2004, they issued a new policy which now invalidated ALL legal marriages…”between two individuals where one or both of the parties claims to be a transsexual”…
Several cases made it to Board of Immigration Appeals (BIA). On May 18, 2005, the BIA issued an Interim Decision (#3512) in the "Lovo-Lara" case in which it upheld the validity of a legal marriage with a transsexual spouse and approved the green card.
This means we're back where we were before the Bush government interfered with the INA by issuing these nonsensical new policies. The immigration services are again supposed to look at the validity of each opposite-sex marriage. After all, a man always had the right to sponsor his female spouse (transsexual or not) and a woman always had the right to sponsor her male spouse (transsexual or not). Keep in mind that transsexual men and women are legally still either male or female which regulates whom they can legally marry.
However, if a transsexual man or woman is in a relationship with someone of the same sex they are stuck just like any other same-sex binational couple with NO RIGHT to sponsor their foreign partner for residency.