The agency says lower sales were recorded in three of the seven subsectors, which together accounted for 51 per cent of wholesale sales.
The motor vehicle and parts subsector recorded the largest decline in March, falling 3.0 per cent to $8.1 billion, the lowest level since September 2012.
The motor vehicle industry, where sales were down 4.4 per cent, accounted for the decrease.
The food, beverage and tobacco subsector rose 1.2 per cent to $10.1 billion, the fifth increase in six months.
Lower sales were recorded in five provinces, which together accounted for 60 per cent of wholesale sales.