NEW YORK (CNN/Money) - TRW Inc. urged its shareholders Monday to vote against Northrop Grumman Corp.'s latest hostile bid, this one worth $6.7 billion, at a May shareholder meeting while the defense and auto parts maker shops itself to other parties.

TRW shareholders will have a chance on Friday to allow Northrop to acquire more than 20 percent of the company. In Ohio, companies are prevented by statute from buying more than 20 percent of a target unless shareholders allow it, TRW spokesman Jay McCaffrey said.

"If Northrop's proposal is approved, it may encourage Northrop to pursue its acquisition of TRW at its current offer," TRW said in a letter to shareholders Monday.

Northrop's current proposal, offering $53 a share for TRW, is inadequate, highly conditional and below TRW's current market prices, the company said. Shares of TRW (TRW: Research, Estimates) are currently trading above $54, while Northrop's (NOC: Research, Estimates) stock rose marginally in afternoon trading.

Cleveland-based TRW has already rejected Northrop's offer twice before. Los Angeles-based Northrop, a defense contractor, initially offered $47 a share, or $5.9 billion, in February for TRW. After that effort was rebuffed, Northrop then raised its offer to $53 a share, or $6.7 billion, in April.

On Friday, TRW said it had entered into confidentiality agreements with several interested parties. Northrop was invited to participate in the process but has so far declined to take part, TRW said Monday.

Northrop has said it would not sign a confidentiality agreement, which would give it access to TRW's books, because of onerous restrictions contained in the contract, including a standstill clause. Such a condition would prevent an interested buyer from pursuing a hostile bid should the target choose another suitor.

TRW is a manufacturing conglomerate whose products include auto parts and equipment for airplanes and spacecraft. A TRW purchase would fill a major hole in Northrop's portfolio, since Northrop lacks exposure to missile defense and military space.

TRW has said that it is in the process of selling its aeronautics business, which is valued at about $1 billion.