Ms Sturgeon said she was "duty-bound" as a constituency MSP
Scotland's deputy first minister is facing calls to resign after writing a letter in support of a man who could be jailed for benefit fraud.
Nicola Sturgeon said she was "duty-bound" as a constituency MSP to make "reasonable representations" on behalf of 60-year-old Abdul Rauf.
He defrauded more than £80,000 from the Department for Work and Pensions.
Scottish Labour leader Iain Gray said Ms Sturgeon had shown an "appalling lack of judgement" and should quit.
First Minister Alex Salmond has defended the Govan MSP's decision to ask a court to consider alternatives to custody in the case.
He said: "This is not a matter connected with her role as deputy first minister but, let me be absolutely clear, I absolutely back her."
Glasgow Sheriff Court heard how Rauf admitted failing to declare a £200,000 property in Edinburgh on his application for income support. He subsequently received £650 a month in rent while he claimed benefits between 2001 and 2006.
Did she have a "duty", as she says, to act as she did?
It might be argued that she had a duty to respond to an approach from a constituent or one lodged on his behalf.
It might be argued further that she did not have to write to the court.
These matters are a question of judgement.
At the same time he was living in a £400,000 house in Glasgow's Maxwell Park area.
In her letter to the court Ms Sturgeon said Rauf had already repaid £27,000 of the money owed and had said he was going to sell one of his properties to repay the rest of the cash.
The MSP for Glasgow Govan, who said she became aware of the case in July 2008, also pointed out in the letter that Rauf had suffered from poor health for a number of years and had a family with children under the age of 10.
She asked the court not to jail him because of the impact that might have on his health and family life.
Sheriff Alan MacKenzie told Rauf that a jail term was "at the forefront" of his mind but said he would defer sentence for three months and released him on bail.
The conviction is Rauf's second for fraud - in 1996 he was given a four-year sentence for stealing nearly £60,000 in pension and benefit payments when he was a sub-post master at Tollcross in Edinburgh.
Ms Sturgeon told the BBC: "This constituent accepted his wrongdoing, he has made attempts to pay back some of the money, but those are matters for the court to take into account.
"I'm duty-bound to make reasonable representations, that's what I did as a constituency MSP, and ultimately it is for the court to make a decision about the disposal of the case."
The SNP have also referred to reports which claimed Gordon Brown also made representations to a court on behalf of a constituent who admitted growing cannabis plants - although the man did not have any previous convictions.
The Conservatives described Ms Sturgeon's intervention as "ill considered" for someone in her position, while the Liberal Democrats said it "beggars belief".