From a CLA Announcement (PDF):
Canada Post will continue to support Canadian libraries by providing the reduced postal rate for mailing printed library materials by libraries to their users and other libraries.
On January 16, 2012, Canada Post will increase Library Book Rates by a weighted average of 5.0%.
There has been no increase in the Library Book Rates since January 2005, despite the fact the inflation rate has risen by an estimated 13.9% since then.
Even with the increase, the Library Book Rates remain very economical and will continue to be substantially lower than the most discounted commercial parcel rates. A 1.28 kg package mailed at the Library Book Rates today costs $0.92 to cover both the sending and returning of the book; this will increase to $0.97 in January 2012. Without the Library Book Rate, the same service of sending and returning of the book would cost $18.00 if mailed at a post office.
Read the Complete Announcement