THINGS ARE heating up in the labor wars at the Goldtex Apartment building in Callowhill, as two union protesters have been arrested for allegedly assaulting a subcontractor working at the mostly nonunion construction site.

Surveillance video shows a scuffle at the work site that ends when two of the protesters use a section of chain-link fence to smash a worker against a stone support that holds up the Reading Viaduct. The worker collapses and lies on the ground for a couple of minutes.

"At least four police officers showed up at this [one] man's house Saturday afternoon and handcuffed him and escorted him out in front of his family and neighbors," said Pat Gillespie, business manager for the Philadelphia Building and Construction Trades Council. The other man turned himself in Monday. "From what I understand, it was a shoving match; there was no damage of any kind," the union leader said.

But Michael Pestronk, one of the brothers who own Post Brothers Apartments, said the contractor was knocked unconscious and an ambulance was called. He said he and his brother Matthew showed video of the alleged July 12 assault to Michael R. Resnick, the city's director of public safety.

"The union has every right to be out there," Resnick said Monday. "They have constitutional, First Amendment rights to protest, to hold up signs. But what they don't have the right to do is to commit crimes, assault people and destroy property."

"No one is subscribing to violence," Gillespie said. "But when you get taunted at and antagonized by people who are helping to destroy all that you work for, you can get aggravated. A pushing match ensued ... but these two guys have now become the No. 1 criminals in Philadelphia."

The Pestronk brothers have been using nonunion labor to renovate the Goldtex factory, at 12th and Wood streets, just above Vine, in a newly trendy loft neighborhood just north of Center City. Some residents are eager to build a park there above the Reading Viaduct similar to the High Line park in New York.

Members of the building trades have protested outside the site for months. Michael Pestronk said the unions turned down an offer to use both union and nonunion workers at the job, a $38 million renovation of a 10-story building.

Recently some residents complained to the Daily News about union tactics. A woman said she found a "nail bomb" in the street. One of the Pestronks said these "bombs" — nails welded together in a ball — have punctured workers' tires.

Meanwhile, the Pestronk brothers filed a complaint with federal officials this month, accusing the unions of violating federal labor laws and also asking for either State Police or federal marshals to enforce a June 12 injunction that orders the protesters to stay at least 15 yards away from the Goldtex entrance.

"They are violating the National Labor Relations Act by blocking our employees and people from getting onto the premises and by trying to discourage vendors and other people from doing business with us," said Charles Ercole, the Pestronks' lawyer. "Sometimes it will take an hour for one of the trucks to go one block when you have 10 union guys walking slowly in the street in front of the truck."