Nicola Sturgeon has said there is a “legitimate” issue about elected politicians holding down second jobs.
The First Minister also said any changes to the system would affect all political parties.
Doubling jobbing is under the spotlight after Tory Owen Paterson was found to have breached lobbying rules while working as an MP and as a paid consultant for two firms.
He stood down from Westminster in the wake of the row, but calls have made for a clampdown on outside earnings.
Paterson earned £100,000 a year for clinical diagnostics company Randox since 2015 and to meat distributor Lynn's Country Foods since 2016.
Although lucrative double jobbing largely affects Tory MPs, politicians in other parties have declared outside earnings in the past.
Between 2015 and March this year, SNP Westminster leader Ian Blackford was chairman of Golden Charter Trust Ltd.
He declared £3,247.25 a month between April 2020 until 31 March 2021.
Asked about politicians and second jobs, Sturgeon said: “I do think there's a legitimate issue about whether people who are elected to serve the public have outside interests that earn them second wages.
“Now, I know people will point to people across all parties, and therefore any party calling for us to address these things has to recognise that it will apply to them as well.”
Holyrood has also faced calls for a clampdown and former MSP Neil Findlay brought forward plans for regulation when he was at Holyrood.
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