City Council appears headed for a showdown tomorrow over whether to allow nonunion labor on the $700 million expansion of the Convention Center, a proposal that could challenge the preeminence of organized labor in Philadelphia for years to come.

Council must approve the operating agreement between the city, state and Convention Center by tomorrow - Council's last meeting of 2007 - or risk losing all convention business for 2011, Council members were told last week.

But the agreement now before Council was amended last week to permit nonunion contractors and their employees to bid and work on the project. The amendment was pressed by Council members unhappy with the level of minority membership in trade unions and with the difficulty in reaching minority-hiring goals without cooperation from the unions.

The amendment is "death language" to union workers, said Philadelphia Building and Construction Trades Council business manager Patrick Gillespie. "Anyone who says they're a friend of organized labor can't be voting for this."

Two Council sources said yesterday that they had at least eight votes for the bill allowing nonunion labor. Nine are needed to pass.

In addition, a leader of the International Laborers Union Local 332, which has a largely African American membership, came out against the amendment.

Black business leaders also cautioned against killing the Convention Center project - and the advances it represented in minority-hiring practices - in a union versus nonunion clash.

Gov. Rendell's spokesman, Chuck Ardo, also weighed in: "The governor does not believe that expanding economic opportunity and supporting organized labor are mutually exclusive goals," Ardo said. "He believes we can and should do both."

The drumbeat was just as intense on the other side. Councilwoman Marian Tasco, who supports the amendment, was to hold a hearing this morning on minority participation in city contracts, and black leaders said they would hold a news conference tomorrow outside Council chambers before the 10 a.m. meeting to call for an investigation of an Oct. 1 incident at the Comcast Center construction site in which a white worker allegedly taunted a black worker with a noose.

Councilman Frank DiCicco proposed the nonunion amendment at a hearing Thursday after he and others accused Gillespie and his member unions of not doing enough to hire minority workers on public-works projects, an accusation Gillespie rejected.

DiCicco sent a letter to Philadelphia AFL-CIO president Patrick Eiding yesterday, warning him that "the Convention Center project may die" if Gillespie "refuses to address Council's very real concerns."

That prospect raised alarms in the minority-business community yesterday.

At a news conference to promote the issue of minority inclusion, business leaders carefully danced around the question of whether they supported the amendment.

"That is not our issue," said public-relations executive A. Bruce Crawley, a long-standing advocate of more minority inclusion.

Developer Kenny Gamble said: "We want to make sure that the baby doesn't get thrown out with the bathwater."

The Convention Center operating agreement's goals of 50 percent hiring of minorities and women for jobs and contracts - and enforcement measures added to the agreement - could be a model for how publicly funded projects get built, Crawley said.

Samuel Staten Jr., president of Laborers International Union Local 332, said he was "totally against" the amendment.

"We will be lobbying the Council all week to take this off," he said.

If a deal was reached that required another amendment to the operating agreement, Council would have to schedule an emergency session to get it done before Dec. 21. Otherwise, new legislation would have to be introduced next year, and it couldn't move through the legislative process before February.

"We'll deal with whatever that amendment says. We just need to get this thing passed," said Albert Mezzaroba, Convention Center president and CEO.

Tom Muldoon, president of the Philadelphia Convention and Visitors Bureau, said pushing the project's completion date to the end of 2010 would jeopardize all convention business for 2011. Conventions lined up for 2010 have already been canceled, he said, and others scheduled for the spring of 2011 would be compromised by a delay.

"Psychologically, you can't just keep going back to customers," Muldoon said. "I don't think we'd have any success in holding the balance of 2011."

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