The SFO is looking into suspected fraudulent trading and money laundering at companies in the GFG Alliance, which includes the Liberty Steel Lochaber smelter and Motherwell steelworks in Scotland.
The probe will also look at the financing that was provided by Greensill, which entered administration in March.
The failure of Greensill had left many fearing thousands of jobs could be at risk, including those at the Lochaber aluminium smelting plant, to which the Scottish Government has provided a £575m guarantee, and the steel plant in Motherwell which received a £7m loan from Scottish Enterprise in 2017, which has yet to be repaid.
Cabinet secretary Fergus Ewing told MSPs in March that Liberty Steel’s Scottish companies were financially sound despite the collapse of Greensill, but there are new demands for him to appear before MSPs again in the wake of the fraud investigation to “end the secrecy” around the deal.
Scottish Labour’s economy spokesperson Monica Lennon said: “This is potentially very serious and heightens the need for a plan to protect steel jobs and vital industries in Scotland.
“SNP ministers must urgently advise the Scottish Parliament what action has been taken to mitigate the risk to jobs in Scotland, following the collapse of Greensill Capital and the difficulties facing GFG Alliance.
“Workers in Scotland cannot be left to pay the price of the Greensill lobbying scandal or poor due diligence. We expect ministers to be open, honest and transparent."
Scottish Liberal Democrat Leader Willie Rennie said the SFO investigation should ring alarm bells in the Scottish Government.
“The Scottish Government’s exposure at the Lochaber smelter runs to hundreds of millions of pounds,” he said.
"We need a full explanation as to how they are protecting the taxpayer from this considerable potential loss. We also need to understand the extent of the due diligence undertaken by the government before they agreed to this considerable arrangement.
"Thousands of jobs were promised, but next to none have been created. The government must end the secrecy.”
Mr Gupta was hailed as the saviour of UK steel in the 2010s when he saved several businesses from possible collapse – most famously in his Tata Steel deal in 2016. But it has since emerged Mr Gupta's companies leaned heavily on Greensill Capital before it collapsed.
The SFO has announced its investigation into “suspected fraud, fraudulent trading and money laundering in relation to the financing and conduct of the business of companies within the Gupta Family Group Alliance (GFG), including its financing arrangements with Greensill Capital UK Ltd."
A GFG Alliance spokesperson said the company would “co-operate fully with the investigation”.
A Scottish Government spokesperson said a ministerial task force and officials had been active throughout the election period, engaging with local management at Liberty Steel, union representatives, GFG and the UK government. “We continue to monitor developments closely,” he said.
“Fergus Ewing delivered a statement to Parliament immediately prior to the election recess and continues to keep members updated.”