Four Legislative Council members are set to make amendments to the bill which was ultimately to enable same-sex marriage registration in Tasmania.

One would allow Tasmanian parents to opt-out of having gender recorded on birth certificates rather than the opt-in proposal under the bill.

Another amendment has proposed the bill be split to treat same-sex marriage and transgender matters separately.

When the government last year brought the bill to the House of Assembly, it had little clue it would be blindsided by another issue bubbling in the background.

The legislation encapsulated changes to a range of state laws: the Adoption Act, the Anti-Discrimination Act, the Births, Deaths and Marriages Registration Act, the Civil Liability Act, the Criminal Code Act, and the Status of Children Act.

Transgender lobby group Transforming Tasmania saw the marriage amendment legislation as an opportunity to solve an issue which had long caused them issues, be it emotional or through something as simple as seeking employment or obtaining a passport.

They sprung into action in over nine months of the year, lobbying any politician they could to seek changes to how gender was recorded on birth certificates.

They won the support of Labor and the Greens in the House of Assembly and ultimately Sue Hickey who crossed the floor to vote against her party on a swathe of amendments. 

Primarily, the amended bill proposed changes that would allow parents to decide whether or not to have a child's gender registered on a birth certificate and for a transgender person to change their birth certificate without a requirement for costly and invasive reproductive surgery.

Attorney-General Elise Archer accused the opposition parties of hijacking the original intention of the bill, saying it would create confusion for the state's registrar, the courts, and had fundamentally eroded parental rights.

As the parliamentary year drew to a close, the heavily amended bill came before the Legislative Council as the last item of business on the final day of the year.

Before a gallery filled with transgender people and their supporters, members - at times emotional and with regret - spoke of their inability to pass the bill without further scrutiny and advice from the state's Office of Parliamentary Counsel.

Premier Will Hodgman on that day had granted members, who wished to make their own amendments, access to the OPC.

All Legislative Council members met in January to discuss the amendments they intended to move to prevent overlap and identify differences.

Launceston independent MLC Rosemary Armitage, McIntyre independent MLC Tania Rattray, Windermere independent MLC Ivan Dean and Murchison independent MLC Ruth Forrest will bring amendments to the floor when debate starts on the bill.

During the meeting, one member said it was identified the issues upper house members had with the bill would have not existed had Labor and Greens been given access to the OPC.

Ms Rattray is understood to move an amendment which will allow a parent to choose to have their child's gender recorded under an opt-out arrangement, rather than the opt-in arrangement in the bill.

This position has been supported by Ms Armitage who will also move her own amendments which include splitting the bill.

"I believe the marriage bill to bring us in line with marriage federally should have been allowed to proceed as drafted and a new bill for the transgender amendments put up allowing adequate time for community consultation on these proposed changes," she said.

"I also believe it is important that gender is included on birth certificates and people have the option of opting out, rather than everyone else has to opt in."

On the topic of birth certificates, she wanted to ensure anyone who considered changing their sex and gender to be absolutely certain of the change and needed to visit two registered medical practitioners before the decision was made.

On the issue of same-sex marriage, she said through community consultation she had been asked asked to keep in the exclusion for people to not solemnise a same sex marriage if it was against their religious belief or affiliation.

Ms Forrest is to move amendments to clear up how data is stored with the state's registrar and clear up confusion in the amendment bill between the terminological differences between sex and gender.

She said she wanted laws to still record the sex of the baby when registered by parents as if they current arrangement.

"The amendments are still keeping with the intent of the bill but with a different approach," she said. 

While dealing with same-sex marriage and adoption issues, the legislation before the upper house comes with the following amendments to birth certificates: