Nicola Sturgeon has warned David Cameron that he must respect the mandate of Scottish MPs at Westminster as the SNP threatened to scupper Government plans to relax the ban on fox hunting in England and Wales.
The Scottish First Minister confirmed that SNP MPs would break with their normal practice of not voting on England-only matters to oppose the proposed change to the law on hunting in tomorrow's Commons vote.
And she warned that her party would be prepared to vote on other issues where Scotland is not directly affected in the months ahead.
Ms Sturgeon directly linked the move to the Government's plans for "English votes for English laws", known as Evel, which would give English MPs a veto over England-only legislation at Westminster.
The decision of the SNP to vote against the legal change - which would actually bring the law on hunting in England and Wales into line with the law Scotland - means it is almost certain to be defeated.
With a number of anti-hunting Conservative MPs planning to vote with Labour and the SNP in the Commons free vote, Ms Sturgeon said it was a reminder to Mr Cameron just how slender his Commons majority was.
"Since the election David Cameron's Government has shown very little respect to the mandate Scottish MPs have. On the Scotland Bill reasonable amendments backed by the overwhelming majority of Scottish MPs have been voted down," she told the BBC Radio 4 Today programme.
"The English votes for English laws proposals brought forward go beyond any reasonable proposition and look to make Scottish MPs effectively second-class citizens in the House of Commons.
"So if there is an opportunity, as there appears to be here, and on an issue where David Cameron appears to be out of touch with majority English opinion as well, to actually remind the Government of how slender their majority is, that is an opportunity we will take."