The Scottish Unionist Association Trust (SUAT) - which has given the party nearly £320,000 - is currently under examination by the Electoral Commission as to whether it is a permissible donor.
Pete Wishart MP has called on the Scottish Tory leader to confirm whether or not donations were used in the 2017 General Election campaigns of MPs John Lamont, David Duguid and Douglas Ross.
Mr Wishart said: “Serious questions are now piling up at Ruth Davidson’s door over the dark money that is funding the Scottish Tories.
“Ruth Davidson must come clean and tell the public if donations from the SUAT were funnelled into the election campaigns of Tory MPs John Lamont, David Duguid and Douglas Ross.
“The Scottish Tories must also reveal if the election expense returns of John Lamont, David Duguid and Douglas Ross were correctly completed.
“It’s time the Electoral Commission used its powers to crack down on rule breaking, cheating and dark money.”
Mr Wishart has also called on the commission to conduct a full investigation into SUAT and its links to the Tories.
He added if any wrongdoing is found sanctions such as the forfeiture of donations and fines should be imposed.
A Scottish Conservative spokesman said: “Since 2001 the Conservative party has declared all donations from the trust in the correct way for permissible donations in accordance with the electoral commission.
“As always, we continue to work closely with the electoral commission on all these matters.”