Statistics Canada says manufacturing sales fell 2.4 per cent in April to $48.2 billion, the fourth decline in five months and the largest monthly percentage drop since August 2009.
The agency says lower sales in the petroleum and coal product and primary metal industries were largely responsible for the decline.
Sales were down in 13 of 21 industries, representing about 86 per cent of manufacturing.
In constant dollars, manufacturing sales fell 1.6 per cent as sales volumes were lower in April.
Sales durable goods declined 1.6 per cent and non-durable goods dropped by 3.2 per cent from March.
Sales fell in eight provinces in April, with the largest declines in Quebec and Ontario, where the bulk of Canada's manufacturing sector is based.