The seasonally adjusted index fell to 55.4 in December from 56.9 the previous month. A reading above 50 indicates an increase in the pace of activity. The unadjusted index fell to 46.7 for 49.2.

Seasonally adjusted, inventories were sharply lower in December from November, contracting to 41.7 from 50.8.

The employment gauge fell to 51.8 from 52.3. Canada's unemployment report for December is due at the end of the week.

Supplier deliveries were up in December, with the index rising to 54.2 from 51.0, while the prices index rose to 54.8 from 53.9.

(Reporting by Solarina Ho; Editing by Peter Galloway)