UPDATE 1-GfK majority owner backs merger with TNS

(Adds details, background, share price)

MUNICH, July 4 (Reuters) - The supervisory board of GfK-Verein, the majority owner of German market research group GfK Holding AG (GFKG.DE), has approved plans to merge GfK Holding with Britain's Taylor Nelson Sofres Plc TNS.L, GfK said on Friday.

The planned merger of TNS and GfK would create the world's second-biggest market research company after AC Nielsen with a value of around $4 billion.

TNS has rejected an improved takeover offer from Britain's WPP Group (WPP.L) worth $2.14 billion, saying it preferred its friendly deal with GfK.

The full membership of GfK-Verein, which holds around 57 percent of the company, is set to vote on the deal on July 21 as the board wants to win the support of members though this is not legally necessary following the board's approval.

Some members such as the city of Nuremberg and the state of Bavaria have taken a critical look at the deal for fear it would lead to job cuts.

Still, Verein Managing Director Raimund Wildner said he was optimistic the deal would win majority approval among members of the association formed in 1934 to promote market research.

GfK shares were little changed at 26.40 euros by 0858 GMT while TNS stock eased 0.2 percent to 242.50 pence.

The deal is being structured as a nil-premium merger of equals in which GfK shares are to be swapped into 11.74 TNS shares. TNS shareholders vote on the plan on July 18.