Unions will be the sole builders of the $700 million Convention Center expansion only if they agree to disclose the demographics of their membership and receive City Council's approval on plans to diversify their ranks, under legislation Council passed last night.

Council withdrew a proposal to open the Convention Center project to nonunion labor and replaced it with one that requires the 17 building trades unions involved in the project to adopt the city's minority hiring goals.

Of the 1,400 workers expected to build the expansion, Council wants 25 percent to be African American; 10 percent Hispanic; 5 percent Asian; and 10 percent women.

Council also demanded that the unions create a combined 350 apprentice jobs for women or minorities, and file quarterly progress reports on compliance with Council.

Those conditions would be incorporated into a project labor agreement between the Building and Construction Trades Council, the Convention Center Authority, and contractors.

And the building trades will have to agree to those conditions for it to go forward.

Frank Keel, spokesman for the electricians union, said after the vote: "The trades appreciate Council's deletion of [Councilman Frank] DiCicco's nonunion amendment. We will reserve any further comment until [Philadelphia Building and Construction Trades Council business manager] Pat Gillespie, the business managers of the member unions, and their attorneys have a chance to thoroughly dissect the details of this deal."

Saying he would not jeopardize a "$700 million gift" from the state, Mayor Street jumped into negotiations yesterday, huddling in Council President Anna C. Verna's office with various Council members and staff.

It was an effort to save the Convention Center expansion - the largest public works project in the history of the state. Whether they have broken that impasse remains to be seen.

Gov. Rendell had called a meeting with all sides for Monday to hammer out a solution. Council members said they still expected that meeting to take place, with the amendment up for discussion.

But the council unanimously passed it, and DiCicco said the Council will accept "nothing less" than the terms called for.

"If they don't accept it, basically, the Convention Center expansion dies," DiCicco said.

Street said last night he expected the unions' approval.

"This is a set of unions that want to do the right thing and see the Convention Center expanded, and I think it's going to be all right," he said.

Council will return in a special session Wednesday to finalize the amendment made to the operating agreement.

Rendell has said he wouldn't release bids for major construction on the project without an agreement. Failure to approve one before year's end would require new legislation next year. That would push the center's completion date toward the end of 2010, jeopardizing bookings in 2011.

In a letter yesterday, Rendell told Council that each month's delay adds $2.5 million in construction costs.

"Any extended delay will make the expansion project so costly that I could not in conscience continue to support the project, considering the additional burden that would be placed on Pennsylvania's citizens," Rendell wrote.

The urgency was created last week, when Council, upset over the building-trades unions' progress on minority hiring and their failure to disclose the racial breakdown of their memberships, voted to allow nonunion contractors to work on the project.

The initial proposal to open construction to non-union contractors - which the unions strongly opposed - was unprecedented in Philadelphia, where labor is a powerful political force.

The amendment also brought concerns from the Convention Center Authority, which has said that a delay in construction would result in loss of business - and credibility.

The center's health is also worrisome to the city's hospitality industry, which sees conventions as powerful draws for its businesses.

Convention Center officials had hoped to send out bids next month and start construction as early as March, with a summer 2010 completion date.

Contact staff writer Jeff Shields at 215-854-4565 or jshields@phillynews.com.