Questions have been raised over the general election expenses of Liberal Democrat deputy leader Jo Swinson in East Dunbartonshire.
Ms Swinson's campaign spending came in £210 below the legal limit, but reports say this was only after almost £7,000 of costs were disregarded.
The SNP said there were "serious questions", with the Lib Dems "living dangerously close to spending limits".
The Lib Dems said they had complied with all Electoral Commission rules.
Her official declaration of expenses was within legal limits, but only after £2,700 of leaflets and other material bought by the party went undelivered - thus not counting towards the total.
A further £4,040 of costs were registered as "national" spending, promoting the party generally rather than Ms Swinson's local campaign.
The SNP said voters would "find it hard to believe that so much cash could be spent on leaflets that just vanished", adding that: "It was an election, not an illusion show."
'Right to know'
A spokesman said: "These revelations raise serious questions over the Lib Dems' campaign in East Dunbartonshire. People have a right to know what has gone on here. They have been living dangerously close to spending limits - and seemingly writing off thousands in costs to keep them within the rules."
However, a spokesman for the Scottish Lib Dems said all spending was above board, and said the SNP were "smarting" after losing 21 seats in the elections.
He said: "All Liberal Democrat candidates follow the clear guidance they are given about election spending, and our party's compliance team are in constant dialogue with the Electoral Commission to ensure that we are abreast of the latest advice and abide fully by all their requirements.
"All expenditure in this election was apportioned correctly and clearly identified in our election return which is now a matter of public record.
"It's understandable that the SNP are smarting from a disappointing result, but they should accept that they were beaten in a fair fight in seats right across Scotland, and concentrate instead on the important business of running the country."