The Army Bomb Disposal Team is examining a suspicious letter addressed to Minister for Justice Alan Shatter.
Gardaí in Rathfarnham in Dublin were called to the local postal sorting office at around 6am.
A staff member at the office became suspicious of a letter addressed to Mr Shatter, which appeared bulkier than expected.
The letter was brought to Rathfarnham Garda Station, which was subsequently evacuated and an Army Bomb disposal Team was called.
The letter does not appear to contain an explosive substance and is to be sent to the forensic science laboratory for analysis.
It is the second such letter sent to Mr Shatter in the last week.
An Army Bomb Disposal Team was called to Mr Shatter's home in Rathfarnham after a similar letter believed to contain baking powder and abusive documentation was found.
Gardaí have begun an investigation and believe both incidents could be linked.