The SNP is calling on David Cameron to "think again" on proposals to give English MPs a veto over legislation which affects only England.
SNP MP Pete Wishart has written to the Prime Minister saying plans outlined in the House of Commons on Thursday are "nothing less than a constitutional outrage".
But Scottish Secretary David Mundell insisted they were "sensible and pragmatic steps" which he said "do nothing" to limit the rights of Scottish MPs to represent their constituents.
It comes after the SNP, Labour and the Liberal Democrats earlier joined forces to condemn proposals from the UK Government to bring in ''English votes for English laws'' (Evel).
The row erupted after Commons leader Chris Grayling announced a new stage is to be introduced for laws passing through Parliament when English, or English and Welsh, MPs will be asked to accept or veto legislation only affecting their constituents before it has its final reading in the Commons.
The changes, which the UK Government is seeking to bring in using parliamentary standing orders, have to be approved in a Commons vote on July 15.
Following the move, Scotland's First Minister Nicola Sturgeon branded the measure a ''constitutional shambles'' which is ''staggering in the extent of its hypocrisy and incoherence''.
Mr Mundell, the only Tory MP in Scotland, has since written to the SNP leader saying Scottish MPs will "still be able to vote on every Bill which passes through the House of Commons".
In the letter, he said: "If the Bill contains elements which do not apply to Scotland, Northern Ireland and, in some cases Wales, an extra stage will be added to the process to allow those MPs whose constituencies are affected to give or withhold their consent to the legislation – effectively, a veto. For those Bills which wholly and exclusively relate to England, the Committee stage will be taken by English MPs only, but with all MPs voting at the other stages.
"These are sensible and pragmatic steps which do nothing to limit Scottish MPs' rights to represent their constituents, but which do give MPs from other parts of the UK the chance to veto proposals which only affect their constituents.
"I believe these proposals will command widespread sympathy and acceptance in Scotland. With our own strong Parliament at Holyrood, which we are making stronger still through the Scotland Bill, to take decisions on matters which are devolved, it is only right and proper that arrangements should be put on place to allow fairness to voters in England."
However, Mr Wishart, writing to the Prime Minister, argued the measures "undermined constitutional integrity and the future of the Union".
He said: "The proposals outlined in the House of Commons on Thursday are nothing less than a constitutional outrage that will see Scottish MPs cut out of voting on matters which impact Scotland and our budget. Quite simply, they will reduce the rights of Scottish MPs to protect the interests of their constituents.
"Your party's attempts to restrict the rights of Scottish MPs at Westminster come at the same time as you propose a totally inadequate Scotland Bill which does not live up to the recommendations of the Smith Commission and fails to understand the changing political landscape in Scotland.
"Last week, 58 out of Scotland's 59 MPs voted to strengthen the Scotland Bill, which means that your support is limited to one single Scottish MP, who is rejecting the views of the other 58.
"And while you plan to introduce an English 'double majority' rule to the Westminster system, the people of Scotland are being denied a double majority to stop Scotland being dragged out of the EU against our will. It seems your party will go to great lengths to avoid having to listen to the needs and concerns of the people of Scotland.
"Indeed, it seems hard to equate your proposals with the stated aims of your party when it comes to the constitutional integrity of the UK. It is difficult to think of any measure more likely to undermine that constitutional integrity and the future of the Union which you claim to support."
Mr Wishart added: "During the referendum, we were repeatedly told by yourself and others campaigning for a No vote that the UK was a 'family of nations' - and each nation had equal standing in that family. In the weeks and months since the referendum, the UK Government has made a mockery of this."
He also wrote that the SNP would oppose the plans at Westminster and asked him to "think again on these disrespectful proposals which are damaging to Scotland".