The move comes as a key advocate of further changes to the law expressed fears the ACT government had rushed its bill through the Legislative Assembly as “a piece of protest legislation” against the new Coalition federal government.

The High Court will hold a directions hearing on Friday after the Abbott government launched a constitutional challenge to the ACT law.

The federal government is arguing the law is in conflict with the federal Marriage Act and the federal Family Law Act and wants a full hearing by late November.

Chief Minister Katy Gallagher said on Thursday the Coalition had moved swiftly to attack the new law and launch what would be “a David and Goliath battle”.

The ACT government has agreed to talks on Monday with constitutional law experts and advocates from Australian Marriage Equality, who argue the law needs further amendments to minimise the risk it will be deemed invalid by the High Court.

The government made some last-minute amendments before the bill was passed on Tuesday, but advice from constitutional lawyers Bret Walker and Perry Herzfeld said the adjustments had not gone far enough to create a separate status of marriage for same-sex couples.

Ms Gallagher said on Thursday the government was open to making further amendments before a full High Court hearing but it remained unconvinced that they were necessary.

The government has also expressed concern that further amendments could water down the law.

In an email to Ms Gallagher on Thursday, NSW MP and former Australian Marriage Equality national convener Alex Greenwich said it was “essential that amendments be made to create a distinct status of marriage called 'same-sex marriage', and that this terminology is consistent throughout the legislation.”

Mr Greenwich said defeat of the ACT law in the High Court would be a major setback for the marriage equality movement in Australia and warned the Chief Minister that “your Government, not the High Court or the Federal Government, will be held responsible”.

“Your legislation must be designed with one goal in mind; to protect the same-sex couples seeking to marry under it,” he said.

“It should not be considered as a piece of protest legislation against the Federal Government.

“I note that your government waited till the Coalition formed government to legislate in this regard, despite having the numbers and a mandate to pass legislation for over a year.

“Had your Bill gone through the same consultation process as the Tasmanian and NSW bills you would likely have been provided with this [legal] advice in advance and it would have informed stronger legislation.”

But Ms Gallagher fired back, writing to Mr Greenwich that his suggestion the ACT law was a “protest” was “simply wrong” and “the claim that we will be held responsible for the consequences of any loss in the High Court is disappointing and unhelpful”.

“The ACT has a long and proud history of eliminating discrimination from the statute book in relation to same sex relationships that exceed 10 years now,” she wrote.

Ms Gallagher told reporters on Thursday it would be more helpful if those in favour of marriage equality worked together to fight the Abbott government’s attack on the ACT law.

“We have seen in the last few days the strength of the Commonwealth attack on this,” she said.

“It is a bit of a David and Goliath battle and I want to make sure that we are in the best position we can be.

“If I am convinced that we need to make amendments to strengthen the bill then we are open to it.”