The First Minister has united with the leaders of the UK Green Party and Plaid Cymru to condemn the UK Government's "toxic rhetoric on immigration".
Nicola Sturgeon signed a joint statement attacking the Conservative party for its "divisive" stance after home secretary Amber Rudd revealed plans to force firms to disclose how many of their workers are non-British.
The statement also suggested Tory rhetoric on immigration could inflame tensions in society.
It was co-signed by co-conveners of the Green Party, Caroline Lucas and Jonathan Bartley, and Leanne Wood from Welsh nationalist party Plaid Cymru.
Speaking at Conservative party conference on Tuesday, the home secretary said measures to curb immigration were necessary to "change the tide" of public opinion and she wanted to "flush out" firms abusing the rules and "nudge them into better behaviour".
Rudd later told BBC Radio 4's Today programme the proposal on foreign workers was "not something we are definitely going to do" but it was "one of the tools" under consideration.
Her plans also include "tougher" immigration rules for international students "studying lower quality courses", suggesting restrictions would give higher-ranked universities an advantage in attracting overseas talent.
In addition to the home secretary's controversial package of measures, the Tory conference heard health secretary Jeremy Hunt announce a strategy aimed at reducing the NHS's reliance on foreign staff.
The joint cross-party response, also signed by Scottish Greens co-convener Patrick Harvie and Green Party leaders in Wales and Northern Ireland, said: "The countries of the United Kingdom face a spiralling political and economic crisis.
"At the top of the Conservative party, the narrow vote in favour of leaving the EU has now been interpreted as the pretext for a drastic cutting of ties with Europe, which would have dire economic results - and as an excuse for the most toxic rhetoric on immigration we have seen from any government in living memory.
"This is a profoundly moral question which gets to the heart of what sort of country we think we live in.
"We will not tolerate the contribution of people from overseas to our NHS being called into question or a new version of the divisive rhetoric of 'British jobs for British workers'.
"Neither will we allow the people of these islands, no matter how they voted on June 23, to be presented as a reactionary, xenophobic mass whose only concern is somehow taking the UK back to a lost imperial age.
"At a time of increasing violence and tension, we will call out the actions of politicians who threaten to inflame those same things."
Prime Minister Theresa May has insisted this week that controls on immigration will be part of Brexit negotiations with the EU, which will begin no later than March 2017.