The ACT Government backed a Greens Bill which gave same-sex couples the right to legally binding ceremonies under the civil union laws the ACT Labor Government introduced last year.

However, the new laws are likely to be disallowed by the Federal Government, which believes such provisions ''undermine and mimic'' marriage between a man and woman. Senator Brown, who is openly gay, said yesterday he would ''find it incredible if Kevin Rudd simply rubber-stamped John Howard on this issue''.

In 2006, the Howard government exercised its power under the Self-Government Act to strike out the ACT's first passage of civil union laws, which included legally binding ceremonies.

Mr Brown said yesterday he would move a disallowance motion in the Senate if the Federal Government again vetoed the civil union ceremony provisions.

''He [Mr Rudd] would genuinely need to inform his Labor representatives in the Senate ahead of time because they will cop it, and I certainly will lead a Senate disallowance motion if it comes to that.'' Senator Brown said it was unreasonable for territory laws to be subject to federal interference.

The ACT Government and Greens believe the legislation passed in the Assembly on Wednesday is consistent with the Commonwealth's constitutional right to legislate exclusively with respect to marriage. Just to be sure, the amendments included a provision that excluded from civil union ceremonies any couple that ''may marry under the Marriage Act''. However, this provision has angered one same-sex marriage lobby group, Equal Love, which argues it could also exclude transgender people.

Equal Love's Canberra spokesman John Kloprogge said, ''Our concern there was that it was unnecessary and exclusionary and would prohibit heterosexual couples and transgender and intersex couples from having access to official ceremonies. ''The ACT Government has taken the wrong policy approach by putting forward a flawed Bill just to appease the Federal Government.''

Greens MLA Shane Rattenbury, who introduced the Bill, said his advice was that transgender persons would not be excluded by his legislation unless they had legally changed their sex, as this would entitle them to enter into a marriage under the Marriage Act.

ACT Liberal senator and former ACT chief minister Gary Humphries said yesterday he would again cross the floor in the Senate in favour of Mr Brown's disallowance motion.

Mr Humphries said his decision had nothing to do with the merits of the legislation.