By Oliver Hirt

ZURICH (Reuters) - A power struggle at Swiss engineering group Oerlikon (OERL.VX: Quote, Profile, Research) intensified after the board proposed measures that could force a full takeover bid from shareholders who accumulate more than a third of the company's shares.

Oerlikon on Friday said that at the upcoming annual meeting in May, its board would propose a bylaw requiring any party with a stake of more than 33-1/3 percent to launch a full takeover bid.

The proposal signals new tensions between Austrian investment group Victory, which controls three seats on Oerlikon's board, and Russian billionaire Viktor Vekselberg, whose investment group Renova controls one seat.

Renova has control of a stake of just under 33 percent in Oerlikon, which makes everything from rocket nose cones to solar cells.

"We interpret this as a defensive move by the board to prevent anyone from taking a controlling stake in the company," said analysts at bank Vontobel in a note.

"Vekselberg's Renova already holds a quarter of the company and probably would like to take under control a further part of Victory's holdings," Vontobel said.

In response, Renova said it did not support the proposed bylaw.

"We are certain that the abolition would not be likely to increase the value of the company for its shareholders," Renova said in a statement to Reuters. "We expect a very serious discussion about this agenda item for the general meeting."