Three post offices have been targeted in separate robberies.
Armed robbers stole a cash bag filled with documents in a raid in Lismore, Co Waterford at 10am on Tuesday.
Two men carrying a gun and a hammer held up and threatened staff in the post office before making off with what they believed to be money.
The pair stole a carrier marked "cash bag" but gardai said it is believed it contained only documents. No-one was injured in the raid.
Gardai said two men aged in their 20s and 30s were later arrested when officers stopped and searched a car in the Dungarvan area of the county.
The suspects are being held under section 30 of the Offences against the State Act, 1939, at Dungarvan garda station.
In an earlier incident, two men armed with knives held up the post office in Avoca, Co Wicklow.
Gardai said the pair threatened staff before escaping on foot with about 2,000 euro in cash. The robbery happened just after the post office opened at 9am and no-one was injured.
In the third raid, also in Co Wicklow, a man attempted to hold up the post office in Arklow.
The incident occurred at around lunch time. It is understood the man fled the scene after spotting gardai nearby.