On April 28, 1928 the Supreme Court of Canada unanimously decided that women were not "persons" and therefore could not be appointed to the Senate. The British Privy Council overturned this decision on Oct 18, 1929.

Source: Library & Archives Canada RG 125, Vol 563, File 5426 

The Supreme Court decision was in response to a petition by five women from Alberta now known as the Famous Five.  These five were perhaps the Mothers of Confederation.