The SNP is being investigated by Scottish Parliament authorities over the potential misuse of postage stamps bought using MSPs' expenses.
The BBC claims that stamps bought on expenses were passed to UK election candidates for campaigning activities, such as sending letters to voters.
The anonymous complaint was submitted to Holyrood's presiding officer Alison Johnstone.
The Scottish Parliament said it was investigating the matter to establish whether there had been any misuse of parliamentary resources.
BBC Scotland News says it has also seen a screenshot from a WhatsApp group, made up of staff who work for SNP MSPs, where there is a discussion about whether or not the stamps can be traced back to the purchaser.
MSPs are allowed to spend up to £5,500 a year on postage and stationery as part of parliamentary resources, external provided by the Scottish Parliamentary Corporate Body
The Scottish parliament’s rules state that they “must be used only for parliamentary duties and must not be used for any other purpose, including party political purposes”.