The law, adopted in October 2016, was introduced after the public voted to accept a popular initiative on the subject – proposed by the right-wing Swiss People's Party (SVP) – back in 2010.
The FSO statistics showed 54 percent of the 1,210 criminals without Swiss passports convicted of a crime in Switzerland in 2017 were handed a mandatory expulsion order.
This suggested that judges were making extensive use of the new law's so-called ‘hardship' clause designed to protect second-generation immigrants without Swiss passports from being forced to leave the country.
The SVP described the figures as an “absolute scandal” and said the hardship clause was being used as a way to get around the new law which makes provision for first-time offenders to be banned from returning to Switzerland for a period of up to 15 years.
But over the course of the day on Tuesday, it emerged the FSO data was skewed, Swiss daily Tages Anzeiger reports.
After justice departments in several Swiss cantons criticised the figures, it became clear that the FSO had, when compiling the data, included types of fraud that are not are not actually subject to mandatory expulsion orders.
Under the new law, only foreigners convicted of tax or benefit fraud are liable to mandatory expulsion but the FSO also included other forms of fraud in its analysis.
The office defended itself saying it had used a literal interpretation of the relevant article in the penal code.
But responding to criticism, the FSO then published separate data on Tuesday including only forms of fraud resulting in mandatory deportation.
This table shows 69 percent of foreigners convicted of a crime in 2017 were subject to a mandatory detention order, and not 54 percent as per Tuesday's figures. A total of 84 percent of those orders were handed down to people sentenced to time in prison.
Meanwhile, the chief prosecutor in the canton of Freiburg, Fabien Gasser noted two years were needed to gain a true picture of how the new law was working. He pointed out that many cases opened in 2017 were still ongoing.
Many simple, quick-to-process cases were included in the figures and these were precisely the cases where expulsion orders were likely to be handed down, Gasser said. For the ongoing, complicated cases, however, those orders were more likely.