The Scottish Government and Scottish Labour will take the unprecedented step of demanding a vote to exclude Scotland from Conservative efforts to amend the rights of trade unions across the UK.

Both parties have taken legal advice to make the UK Trade Union Bill subject to a legislative consent motion (LCM), normally reserved for Westminster legislation impacting on Holyrood powers.

Employment and industrial relations are reserved to Westminster, but Holyrood's two biggest parties say Scotland should have an LCM veto over the Bill's implementation in Scotland.

Conservative MSP Murdo Fraser attacked the Scottish Government for bringing forward a debate on an issue reserved to Westminster, a week after MSPs considered the future of Trident.

In a debate in Holyrood, Fair Work Secretary Roseanna Cunningham said: "I have asked the UK Government to exclude Scotland from the Bill in its entirety.

"However if they are unwilling to exclude us I have now also made it clear that the UK Government should seek the consent of the Scottish Parliament before attempting to impose this ill-thought through legislation in Scotland.

"I have asked our legal advisers to explore several possible bases for a Legislative Consent Memorandum and Motion."

She highlighted UK Skills Minister Nick Boles's suggestion that secretaries of state should be empowered to make employment regulations in their portfolios, and suggested this should apply to Scottish ministers with devolved portfolios such as health and councils.

She also pointed out that the Bill would impact on employment contracts and industrial relations in devolved public authorities, and breach the European Convention on Human Rights which is enshrined in Scots law.

She added: "All of these issues may give grounds for the Parliament to seek consent, but we must be aware that this is uncharted territory.

"We have never before been in the position where both the UK and Scottish governments have not had an agreement on issues of legislative consent."

Labour opportunity spokesman Iain Gray has sought his own legal advice from Patrick McGuire, of Thompsons Solicitors, who backed the cross-party call for an LCM.

In an email to Mr Gray, Mr McGuire said: "The Trade Union Bill significantly impacts upon and undermines the Scottish Government's executive power and competence in relation to employing their staff.

"Accordingly, in that context the Scottish Parliament should certainly have the right to debate an LCM on the relevant provisions on the Trade Union Bill."

Mr Gray said he has now written with this advice to the head of the parliamentary business team and asked the clerks to investigate whether an LCM would be relevant in the context of the Trade Union Bill.

He said: "I believe that it is competent and required. If it is, I would propose to bring one forward at the earliest opportunity, or indeed to support the Government should they feel able to do that to."

Mr Fraser said: "For the second week in a row we're devoting a large part of Tuesday afternoon to discussing a matter which is properly the responsibility of another Parliament and where the matter is currently being actively debated.

"Is there any reason why the Scottish Government is spending so much time talking about reserved issues? Could it possibly be that its record on devolved matters is such a dismal one?

"Whether that's in the area of education, or the health service or justice, the list of failures is piling up.

"Why are we not spending our time discussing those matters rather than matters that are properly the reserve of Westminster?

"This chamber should not be duplicating the work of the House of Commons."

On the substance of the Bill, he added: "There are numerous examples in the past of strikes in essential services that have gone ahead with a very poor level of support from members.

"Because of the public inconvenience, there's a clear public interest in ensuring that strikes which are held do require substantial support within a trade union."