The British Government would expect passport checks between Scotland and England if a looser immigration policy is adopted north of the border after independence, according to Home Secretary Theresa May.
Her view is at odds with the Scottish Government's aim of keeping passport-free travel across the UK and Ireland.
She warned that the SNP administration's pledge to pursue "healthy population growth", outlined in the White Paper on independence, will "undermine" Tory policies south of the border.
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"If the people of Scotland vote to leave the UK there would be profound changes for migration policy," she said in a speech at the Scottish Conservative Party conference in Edinburgh.
"An international border would be created where one does not currently exist. This would have implications for people travelling to visit family, go on holiday or do business, and for our economies more generally.
"Buried deep in Alex Salmond's White Paper is the admission that, just like the last Labour Government, a separate Scotland would pursue a looser immigration policy.
"That would undermine the work we have done since 2010, and the continuing UK could not allow Scotland to become a convenient landing point for migration into the United Kingdom.
"So that would mean border controls between a separate Scotland and the United Kingdom. Passport checks to visit friends and relatives. A literal and figurative barrier between our nations."
The White Paper, published in November, criticises the "go home" policy of the Conservative-led Government at Westminster.
It states: "Scotland has a different need for immigration than other parts of the UK. Healthy population growth is important for Scotland's economy.
"One of the main contributors to Scotland's population growth is migrants who choose to make Scotland their home.
"In future our enhanced economic strategy will also do more to encourage young people to build their lives and careers within Scotland and to attract people to live in Scotland."
The White Paper also sets out the aim to stay in the Common Travel Area (CTA) across Britain and Ireland.
It states: "We plan to remain part of the CTA which means that there will be no border controls, and you will not need a passport to travel to other parts of the UK, Ireland, the Channel Islands and the Isle of Man."
The Scottish Government does not want to sign up to the Schengen free-travel area, which suspends border controls between EU countries. The UK and Ireland opted out of the scheme, while keeping its own distinct agreement.