The UK Government has been urged to "get to grips" with the problem of extra charges for mail order delivery to the Northern Isles.
The cost of some mail order services was branded "outrageous"
Orkney and Shetland MP Alistair Carmichael claims deregulation of parcel post has even seen some firms refusing to deliver to islanders.
He has called on Trade and Industry Secretary Patricia Hewitt to intervene.
The minister pledged to follow up the issue but Mr Carmichael has called on her to give a clear lead.
Speaking in the House of Commons, the Liberal Democrat MP said: "Since deregulation of parcel post we have seen an increasing practice - particularly among mail order companies - of either refusing to deliver addresses off mainland Britain, or else to charge extra for it.
He asked the secretary of state to "get to grips with this particular issue to ensure that people in island communities can enjoy the same level of service as those on the mainland".
Ms Hewitt responded: "There has always, of course, been a problem in meeting quality of service targets in those most remote communities - particularly in the island communities.
"That is an issue which I know the post office management are working on and it is certainly one that I will draw to the attention of them again."
Speaking after the debate, Mr Carmichael said he had received a steady stream of letters from constituents who had been told by companies that they would not deliver to the Northern Isles, or charged extra.
"In one case this amounted to an extra £75," he said. "The government needs to give a clear lead on this. Many people in the Isles depend on mail order companies.
Mail order can be a boost to remote communities
"I fear that Patricia Hewitt's answer today demonstrated that she does not understand what this issue is about."
One company cited by a constituent of Mr Carmichael was Postscript, which provides mail order books.
Spokeswoman Juliet Morgan said they had experienced surcharges sending out orders offshore which forced them to pass this on to customers, but had since changed carriers and moved to send lighter items through the normal post.
She said: "We are a small company but have found that we can charge a flat rate now for smaller packages, so we recommend our customers split their orders if they are buying several items or heavier items."
Dr Tom Begg, chairman of Postwatch Scotland, said it was a serious issue, especially with heavier items.
He said: "It is a long standing problem which is causing very real concern.
"When you look at the relative costs, some purely commercial enterprises either charge outrageous prices or decline to deliver at all.
"You can send the lighter stuff through Royal Mail, but with deregulation the problem comes with heavier stuff and we're not happy with the situation."
A short debate on the issue is due to take place in the House of Commons next month and Postwatch said it was also following up the situation at Westminster.