Allegations have been made over an MP's expenses
Edinburgh South MP Nigel Griffiths is facing mounting pressure to resign over reports that he claimed £40,000 in allowances to cover the cost of renting an office he already owns.
The minister for small business, who denies any wrongdoing, is alleged to have used the money to help his autistic sister.
Tayside North MP Pete Wishart said: "He should submit his resignation as a government minister and fully co-operate with the standards commissioner as she investigates these allegations into his conduct as an MP."
Shadow Scottish Secretary Jacqui Lait was also writing to Mrs Filkin on Monday seeking an investigation.
Mr Griffiths bought his Edinburgh office in 1997 with money from a legacy and is said to have claimed up to £10,000 in rent allowance every year since then from the Commons authorities.
The cash goes to a trust fund to provide holidays and treats for his autistic sister.
His critics said the issue was not the use of the money but that he seemingly failed to detail the arrangement in the register of MPs' interests.
They say he has broken the rules and that he should step down as minister.
Ms Lait, the Tory MP for Beckenham, said she wanted to ensure that Mrs Filkin was aware of the allegations.
She said that she wanted to know why the ownership was not registered, who received the rent from the Westminster Fees Office, why it was not declared in the register of interests and whether there were any tax implications.
Liberal Democrat Marilyn McLaren, who stood against Mr Griffiths at the last general election, said the issue should be referred to the standards committee in Westminster "as a matter of urgency".
Denied wrongdoing
"I do think Nigel Griffiths, if the allegations are found to be true, should resign as minister and consider his future as the MP for Edinburgh South," she said.
Mr Griffiths is also reported to have received £4,000 from the Edinburgh South MSP Angus Mackay for sub-letting part of the constituency office.
However, he denies any wrongdoing and said he had written to the Commons fees office to have the matter clarified.
Mr Griffiths said: "I have already written to the Fees Office on this matter and I am confident that the financial arrangements I have in place will be acceptable.
"I am seeking to get written confirmation of this as soon as possible."
The row comes just weeks after former Scottish First Minister Henry McLeish resigned following the so-called Officegate scandal surrounding his own constituency office.
And last Sunday questions emerged over the office arrangements of two other Labour MPs, prompting the party to order all Scottish MPs to examine their books.
Eastwood MP Jim Murphy admitted that the Commons had paid the full rent for his constituency office while he claimed half the rent from the local MSP Ken Macintosh, who shares his office.
Russell Brown also had the rent for his constituency office paid in full while receiving extra rent from Dumfries MSP Elaine Murray.