Rishi Sunak has been blamed for postal vote delays that have left some in Dundee, Fife, Perth and Angus unable to cast their ballot.
Many local authorities have taken emergency action to ensure Scots can still have their say, but some have already travelled overseas.
They will be unable to vote, with emergency proxy arrangement only available in specific, limited circumstances.
SNP leader and First Minister John Swinney said the problem revealed that Rishi Sunak did not consider that the election falls at the beginning of school summer holidays in Scotland.
Mr Swinney added: “I warned when the election was called that it was going to take place during the Scottish school summer holidays and many of our schools broke up for the summer last week.
“Those postal ballots have not arrived with people and some of them have now left the country, and they have been disenfranchised because of the timing of the election, which is something I deeply regret.
“I warned about the decision to have the election during the school holidays and welcome the fact that a number of local authorities in Scotland have taken emergency measures to establish centres which could enable people to exercise their postal vote.”
The Scottish Greens also placed the blame at Mr Sunak’s door.
The party’s co-chair, Ross Greer MSP, pointed out that disenfranchised voters could be a deciding factor in some seats.
Mr Greer said: “There are obviously important administrative lessons to be learned here. But the problems come back in large part to Rishi Sunak’s selfish timing of the election.
“The Prime Minister could have called it at any point between now and January, but he chose the most inconvenient week of the year for people in Scotland to vote.
“Our school holidays start at the end of June, so this decision predictably resulted in a surge of postal vote applications.
“[Mr Sunak] and his team either didn’t care to check or they knew and proceeded anyway.”
What can you do about a missing postal vote in Dundee, Fife, Angus and Perthshire?
Completed postal votes must have reached councils by 10pm on polling day, July 4.
They can be returned by post or handed in at council offices and can also be dropped at the correct polling station on election day.
Over the weekend Fife Council allowed voters who would not be at home this week to collect a replacement ballot at Fife House.
Ken Gourlay, Fife’s Returning Officer, said a high volume of people had been helped, with over 200 ballot packs issued.
Mr Gourlay said the council expected all postal votes to arrive by Monday.
He added: “If you registered for a postal vote before the deadline of June 19 and still haven’t received it in the mail on Monday, email postals@fife.gov.uk and we’ll make arrangements with you.”
The Courier understands Dundee Council is also preparing to announce arrangements for those who have not yet received their ballot or need to be reissued with one urgently.
Anyone impacted can email ero@dundeecity.gov.uk or telephone 01382 434444 for advice. Ballots can also be returned to the box office in City Square, open Monday to Wednesday between 9am-5pm.
In Angus, ballots can be returned to Angus House, Forfar. Anyone who has received their voting pack can email elections@angus.gov.uk.
In Perth anyone without their ballot by July 1 is asked to email elections@pkc.gov.uk.
Can I apply for a proxy ballot?
There are limited circumstances, set out in law, in which someone can apply for an emergency proxy.
These include a medical emergency, travelling for work or losing your photo ID.
The Electoral Commission has confirmed to The Courier that missing your postal ballot because you are travelling abroad for a pre-planned trip will not count.
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