UPDATE 2-Mobis shareholders balk at Hyundai Motor Group overhaul plan

* Plan passes Mobis's cash-cow business to Glovis-analysts

* Mobis investor says will vote against plan

* Hyundai Motor, Mobis and Kia shares fall (Recasts with investor concerns, adds investor comment, background, updates share prices)

SEOUL, March 29 (Reuters) - Investors wiped almost $2 billion off the market value of South Korea's Hyundai Mobis on Thursday amid concerns a proposed restructuring of Hyundai Motor Group would benefit the controlling family ahead of shareholders.

The parts supplier's shares fell as much as 8 percent in morning trade as investors fretted it may be forced to hand over its lucrative business to affiliate Hyundai Glovis too cheaply as part of the structural overhaul.

"This is passing too big a piece to Glovis," said a fund manager who holds Hyundai Mobis shares, requesting anonymity because he was not authorised to speak to the media. He said his company would vote against the spin-off plan.

Hyundai Motor Group, South Korea's second-biggest family-owned conglomerate after Samsung Group, said on Wednesday it planned to streamline its complex ownership structure in response to pressure from the government and investors.

The chief of South Korea's antitrust agency, Kim Sang-jo, said the plan was a "positive" step towards improving the group's ownership structure.

Under the plan, which needs the approval of both companies' shareholders on May 29, Hyundai Mobis will spin off its domestic module and after-service parts businesses and merge them with logistics affiliate Glovis.

Mobis shares clawed back some losses and were down 3.8 percent at 0345 GMT. Hyundai Glovis shares were up 6.3 percent, having earlier surged as much as 23.6 percent to their highest intraday level since Oct. 2015.

Glovis is personally backed by the auto-to-steel group's controlling Chung family, with Chairman Chung Mong-koo holding 6.7 percent and his only son, Vice-Chairman Chung Eui-sun, holding 23.3 percent.

The Chungs plan to sell their shares in Glovis to buy stakes in Mobis, a de facto holding company at the top of the group's ownership structure. Affiliates Kia Motors, Glovis and Hyundai Steel will reduce their stakes in Mobis as part of the exchange.

"All that will be left to Mobis is a shell of a business. There's no reason for Mobis shareholders to agree to the spin-off at this rate," Lee Jae-il, analyst at Eugene Investment & Securities said.

In addition to resolving the group's cross-shareholdings in response to regulatory pressure, the restructuring plan also paves the way to building up capital for the junior Chung to ultimately gain control of the group, investors and analysts said.

The domestic after-service parts business that will pass from Mobis to Glovis is a stable cash cow, and without it Mobis could find it hard to fund development of autonomous driving and electric car technology, said Lee from Eugene Investment & Securities.

Other major group affiliates lost ground, with Hyundai Motor falling 6 percent and Kia Motors down 5 percent.

(Reporting by Hyunjoo Jin and Joyce Lee, Additional reporting by Dahee Kim; Editing by Stephen Coates)