The agency says five of seven subsectors, representing 85 per cent of total sales, reported declines.
In volume terms, wholesale sales were down 0.3 per cent in July.
The largest sales decrease in dollar terms was in the food, beverage and tobacco subsector, where sales fell 1.5 per cent to $9.3 billion in July mainly due to weakness in the food industry.
Sales of agricultural supplies computers and communications gear and motor vehicles and parts were also down.
Wholesale sales fell in six provinces in July, with Ontario, Quebec and Manitoba accounting for most of the national decrease.