Official statistics showed that between January and March 7,098 people were naturalized in Switzerland – 3,080 fewer than the year before, the Swiss news agency SDA reported.
The decline affected both regular and simplified naturalizations – which applies to foreign nationals with a Swiss spouse or partner – according to the State Secretariat for Migration SEM.
It is not clear why the number of people becoming Swiss has dropped so dramatically.
But the SEM believes it is likely to be a temporary fluctuation and not a general trend.
A number of changes were introduced to the naturalization process from the start of 2018 – including standardized language requirements – but the impact of those will not be seen for some time.
The citizenship process in Switzerland is a laborious process that can take up to three years to complete.
Among the different European nationalities, Italians and Portuguese saw the biggest drop in naturalizations – 51 percent and 48 percent respectively. There were also big declines in the number of French and Spanish becoming Swiss.
The figures showed a slight drop in migration to Switzerland compared with last year and a rise in those leaving Switzerland for other countries.
The SEM said this was partly due to the attractive labour markets in Germany and France.
At the end of March there were more than two million foreign citizens resident in Switzerland, of whom two-thirds came from European Union and EFTA countries.