The revised cash-and-stock offer announced Monday valued Washington Group at $97.89 per share, an 8.5 percent increase from $90.20 per share, or $3 billion, before the new terms were revealed. Washington Group shareholders would wind up with a 35 percent stake in URS instead of 32 percent under the original offer.

The changes apparently weren't enough to impress investors. Washington Group shares shed 27 cents to $95.88 Monday, while URS shares fell $1.55 to close at $58.55.

San Francisco-based URS is hoping its new offer will be enough to satisfy Washington Group shareholders who had vowed to block the proposed sale unless they were paid more.

The backlash prompted both URS and Boise, Idaho-based Washington Group to postpone Oct. 30 meetings set up to gain shareholder approval. The companies will now ask shareholders to accept the higher price at Nov. 15 meetings.

URS and Washington Group first agreed to join forces in late May. At that point, URS' bid valued Washington Group at $80 per share, or $2.6 billion.

But the price rose as URS shares climbed, making the stock portion of the deal more valuable. Washington Group's shares appreciated at a more rapid clip as investors became increasingly bullish about the company's prospects.

When it became apparent that Washington Group stood to make more money on its various projects than previously envisioned, shareholders began to demand a higher price from URS.

Greenlight Capital Inc., which owns a 10 percent stake in Washington Group, came out against the deal in July. The New York-based investment company believes Washington Group is worth $117 per share.

Schultze Asset Management, which owns about 3 percent of Washington Group's stock, filed a lawsuit in Delaware last month in an effort to block URS' sale.

A major advisory firm, Institutional Shareholder Services, also opposed the deal.

Three other advisory firms -- Glass Lewis, Proxy Governance, and Egan-Jones -- had recommended Washington General's shareholders accept URS' original offer.