The arrests were the result of a joint operation between Swiss and Italian police investigating people smuggling from the Italian city of Como into the Swiss canton of Ticino, reported news agencies.
The four suspects, aged from 21 to 39, are legal residents of Italy.
They are accused of demanding payment of 90-150 euros per person to help migrants illegally cross into Switzerland, driving them to Lugano or even as far as Zurich.
The police operation dates back to October, when investigators identified a vehicle that had crossed the border at Ronago, west of Como, 45 times in a month.
A 23-year-old Ghanaian woman was arrested in December, while three other people were taken into custody on Friday.
The Swiss-Italian border is a popular crossing point for migrants travelling from Greece and Italy.
Migrants are allowed to pass into Switzerland if they claim asylum at the border. However many do not want to stay in Switzerland but wish to transit through the country on their way to Germany, preferring to seek asylum there. But in that case Switzerland does not consider them to have refugee status, and therefore sends them back to Italy.
Last July the Swiss border guards were criticized by Italy for refusing entry to migrants who did not want to claim asylum, causing an overflow of people stuck in Como after being turned away by Switzerland.
However the Swiss border agency said Switzerland was simply following the rules of a readmission agreement with Italy.
At the time, the number of migrants attempting to cross into Switzerland was at a record high, but that has since fallen.
In September a Socialist Party MP was arrested at a border point in Ticino for allegedly helping migrant children cross illegally into Switzerland.
Legal proceedings are ongoing against Lisa Bosia Mirra, who in December was part of a group of volunteers awarded a 12,000 franc prize for providing hot meals to migrants in Como "and accompanying them to the Swiss-Italian border", Ticino Online reported.
In January the number of people lodging a request for asylum in Switzerland was 1,588, 10 percent fewer than in December and 56 percent fewer than in January 2016, according to the Swiss migration office (SEM).