Exchequer returns for August show a significant fall in revenues collected during the month.
Total revenues of €2.4 billion were almost €200m, or 7.4%, below target.
Most of the shortfall came from income tax, which was €98m below target for the month, and excise, which was €97m below target.
Compared with August last year, the inflow of revenue was some €372m - or 13.3% - lower.
Stronger performance earlier in the year means the overall amount of revenue for the first eight months of the year is €450m - or 1.6% - ahead of target, and is up 6.2% compared with the same period last year.
Commenting on the figures, Tax Partner at Grant Thornton Peter Vale said: "We are so used to strong Exchequer figures every month that today’s figures look a little disappointing.
"Of particular concern is lower than expected income tax receipts, coming in at 6.5% below target as well as being behind last year.
"This could just be a one off blip; it is certainly too early for it to be Brexit related. It also goes against much of the recent positive news in relation to jobs announcements. However, coming so close to the October Budget, it is of concern.
"Excise duties are also significantly behind target (19.6%) due to weak tobacco receipts," Mr Vale added.
