The gangs are filling adulterated liquor in branded liquor bottles and selling them.
The smugglers were held on Monday with liquor and beer worth Rs 22,382 in the border area of Nadia district, said the BSF.
According to Excise Deputy Commissioner T A Ashok Kumar, an officer of Circle Inspector rank has been assigned to investigate the case.
After the rats ate up some portions of the packet, the India Post officers detected the mischief. The incident was reported on Tuesday when India Post officials alerted the Excise department.
The lockdown has led to an increase in the illegal sale of alcohol, especially ale and arrack, say residents of Villupuram.