From the Queen Mary Website:
"January 1, 1934: The effective date for transferring the assets of the Cunard Steamship Company and the White Star Line, to the newly formed Cunard White Star, LTD. Cunard was credited with 62 percent of the share capital, and White Star with 38 percent."
Initially, the Queen Mary's keel was laid and work begun in 1930. However, due to the effects of the Great Depression, work was suspended in 1931. The following year, the British government announced it would subsidize the building of the ship--along with another, the Queen Elizabeth--on the condition that the Cunard and White Star lines merge. The two companies agreed and building resumed in 1934.
Queen Mary by James Steele