Scottish Secretary Alister Jack wrote to the Scottish Government with concerns about the legislative competence of the United Nations Convention on the Rights of the Child (Incorporation) (Scotland) Bill before it was passed last month.
Mr Jack said the Bill could potentially put legal duties on UK ministers, which would be outwith the remit of the Scottish Parliament.
However, none of the requested amendments were made to the legislation, which Mr Jack announced he would refer to the Supreme Court on Monday along with the European Charter of Local Self-Government (Incorporation) (Scotland) Bill, proposed by independent MSP Andy Wightman and also passed unanimously, over similar concerns.
First Minister Nicola Sturgeon called the move “morally repugnant” as the SNP accused the UK Government of trying to strike down a law to protect the rights of children.
Mr Jack has repeatedly stated the issue with the legislation is purely based on the possible overreach of the Scottish Parliament, not the contents of either of the Bills.
On Tuesday, Mr Swinney continued the spat, pledging the Scottish Government would take the fight to court if necessary and urging opposition parties to support their plight.
“Only the UK Tory Government could take issue with legislation which builds children’s rights into the fabric of decision-making in Scotland, and shifts power out of the hands of ministers and into the hands of children themselves,” he said.
“This shows a stark contrast between an SNP Government committed to protecting the rights of every single person who lives here – and a Westminster Government which wants to block world-leading legislation so that they can continue doing things which violate the rights of children and young people under the UNCRC.”
He added: “If re-elected, I commit to commencing every part of this legislation that I can. Where we are legally prevented from doing so, we will see the Tories in court.
“The Scottish Tories, and other opposition parties, now have a choice to make – will they side with Boris Johnson’s miserable attempts to breach children’s rights – or will they side with Scotland’s children, and commit to protecting the Bill that they voted for?”
A UK Government spokeswoman said: “The UK Government Law Officers’ concerns are not about the substance of the legislation, rather whether parts are outwith the legislative competence of the Scottish Parliament.
“As with every Bill passed by the Scottish Parliament, there is a four-week period where the UK Government law officers can exercise their discretionary powers under section 33 of the Scotland Act 1998 to refer the matter to the Supreme Court.
“For the UNCRC Bill, that four-week period ended on April 12, 2021. This is the same day the UK Government filed papers with the Supreme Court.”
A Scottish Conservative spokesman said: "This legal case is entirely about the way in which the legislation is drafted and not its substance.
"The dishonest SNP know we support this law. We warned them about this issue, yet they deliberately sought to manufacture a fight with the UK Government which is typical of their nationalist grievance politics."