A complaint has been made to police about Liberal Democrat deputy leader Jo Swinson's election expenses.
The East Dunbartonshire MP is understood to have been reported by one of her constituents.
Police Scotland confirmed it had received a complaint and said officers were investigating.
Swinson reclaimed her seat in June's snap general election after losing it to the SNP after a decade in 2015.
The East Dunbartonshire constituency was one of the top Lib Dem targets in Scotland this year.
'We have full confidence that there is no substance to this complaint.'Lib Dem spokesman
A spokesman for the Liberal Democrats said: "We have full confidence that there is no substance to this complaint.
"We make no apology for fighting as hard as we could to stop the SNP in their tracks. The people of East Dunbartonshire made a clear choice when they rejected the SNP in June.
"This is a classic SNP tactic when they have lost an election. Last year, they wasted 13 months of police time with their complaint about the election in Edinburgh Western and the police found there was no case to answer."
Police Scotland investigated claims regarding Lib Dem MSP Alex Cole-Hamilton's expenses from the 2016 Holyrood election.
The Crown Office later decided he would not be prosecuted.