A Green MSP has urged the Scottish Conservatives to "come clean" over a £100,000 donation given to the party by a supporters group.
Ross Greer 's call comes after it emerged the party was handed the six-figure sum last year by an unincorporated association called the Irvine Unionist Club, an unregistered donor.
Under electoral law, unincorporated groups must be registered with the commission if they donate more than £25,000 in a single year.
Greer has now lodged a motion at the Scottish Parliament calling on the party to clarify who the association are and how they got the sum of money.
There is no suggestion the party has broken the law as the duty to register lies with the association.
The nature of the donation came to light following an investigation by the Open Democracy website.
Greer said: "We need the Tories to come clean about this donation and answer questions. Where did the money come from? What was it used for? Why was the donor not registered?
"In a democracy we have a right to transparency in political donations, this protects us from having a system in which rich interests can influence the system from behind a veil of secrecy.
"The current system is not fit for purpose - it's laughable that it should take an investigation by journalists to unveil something that raises so many questions. The government needs to bring in a new system quickly."
The Electoral Commission is establishing the facts of the matter before it chooses whether to drop or take the probe further.
A spokesman for the Scottish Conservatives said donations to the party are "properly and transparently declared" and they have "not been contacted by the Electoral Commission on this matter".
In response to Ross' motion, he said: "Political parties and their accounting units are legally required to report donations that they receive over a certain threshold.
"In this case, the accounting unit [the Scottish Conservatives] has met its obligations.
"As an unincorporated association, the donor should have applied to register with the commission when making the donation."