The two companies reached a preliminary agreement for a paper-and-cash deal for Fiat Industrial to buy the 12 percent of CNH it did not already own on Nov. 19. The merger, now approved, will be effective in the second quarter of 2013.

The two groups will be merged into a newly-formed company in which CNH shareholders will receive 3.828 shares, and Fiat Industrial shareholders one share.

The new company - which has not been named yet - will move its main listing to New York, and will "use its reasonably best efforts" to keep Milan as a secondary listing. Fiat Industrial was spun off from sister company Fiat in 2011 and is controlled by Italy's Agnelli family.