Except for two construction trucks and a crew of five workers standing around shooting the breeze, the parking lot at the King of Prussia Plaza was nearly empty just after 7:10 a.m. Wednesday.

An unlikely place for a beating, but two of the five men were attacked with punches and bats, and Upper Merion Township police are still trying to figure out by whom and why.

Suspicion is centering on union ironworkers opposed to nonunion workers on the construction site of a new Toys R Us, but as of late Friday afternoon, there had been no arrests, and no one had been identified.

Union officials insist their workers had nothing to do with it.

"We have picket lines all the time," said Joe Dougherty, business manager of Ironworkers Local 401. "We know what you have to do. You can't have any violence on the picket line.

"They are insinuating that because we were picketing there, we were involved in this," he said, "but we definitely were not. We're not picketing the nonunion guys. They have to make a living, too."

Wednesday started out rough.

When Enrique Farias, 34, and Chris Mengel, 35, and the three other steelworkers from Maura Buildings Inc., a nonunion contractor in Lebanon, drove up to begin work at the Toys R Us site, Local 401's pickets blocked the drive.

Instead of forcing their way in, Farias, Mengel, and the others decided to wait nearby, in the mall parking lot.

"We were just waiting for the police to show up and talk to them so we could go back and work our day," said Farias, who was taken to a nearby hospital for treatment after being hit on his head, back, leg, and side, and was later released.

"We were there two or three minutes," he said. When a black, four-door Chevy sedan pulled up and four men jumped out with bats, yelling and shouting, three workers ran away. Farias said he hopped into the passenger seat of one truck and Mengel, the son of Maura's owner, ran to the driver's seat of the other truck. The men shattered the trucks' rear windows with the bats.

Farias jumped out, and one of the men began to hit him.

Farias said he managed to get the better of one attacker, but two others started pounding him with the bats. Mengel, who was also hit, used his cell phone to photograph the assailants and their car. Police released that photo. Dougherty said he did not recognize the car or the people in it.

"This is the first time anything like this has ever happened to me," Farias said. "I'm a peaceful guy. I've never even been in a fight."

Farias said he could not be sure whether the men who attacked him were union members. "I'm not directly saying that, but I do think it comes from that."

Kane Builders Inc. in Glenside is the general contractor at the four-acre site, and the subcontractors are both union and open-shop. The site-preparation subcontractor is union, as is the framing subcontractor, said Mark Spencer, Kane's site supervisor. Ironworking and masonry are nonunion.

Paul Daily, Maura's project manager, said that Local 401 had asked Maura to include a union worker on its crew but that Kane and Toys R Us, which have oversight, refused.

Such requests are common, Daily and Dougherty agreed. For example, Daily said, Maura will add a union ironworker to its crew on a Cherry Hill job.

Trouble in toyland started in late May after Maura delivered anchor bolts to the job site. The bolts, sunk in concrete, are used to attach steel columns to the foundations. After the masons installed them, vandals bent or broke 120 bolts, Daily said.

Maura's crew began work on June 17. Over the weekend of June 19, wires were cut on a forklift, making it inoperable. Pickets went up Monday, and the other union subcontractor honored the line.

Police are continuing to investigate.

An injunction was obtained late Tuesday but had not been read to the pickets Wednesday morning, Spencer said. Construction resumed Wednesday afternoon and continued through the week.

Picketing on construction sites is common, but violence is rare, said Geoffrey Zeh, president of the Southeast Pennsylvania Chapter of Associated Builders and Contractors, a generally nonunion group.

"We haven't seen that kind of activity in the last few years," he said.

"I don't like to point fingers until there's more information. It may or may not be conclusive. Sometimes there is a disgruntled member, and it has nothing to do with the union. Or it could be someone who has nothing to do with the union at all."

In 1972, the King of Prussia area - not far from the Toys R Us site - was the location of an infamous incident of construction-union violence.

On June 5, about 1,000 men, many wearing hard hats, swarmed over the construction site for a hotel and theaters complex in Valley Forge, now the Valley Forge Convention Center and a hotel.

The men firebombed it, causing an estimated $300,000 to $400,000 in damage. Sixteen were convicted and 11 jailed.

Mengel could not be reached for comment on Friday.

Farias said that he had been accepted as an apprentice in an ironworkers local in California, where he lives with his wife and three children. But he could not find an employer to sponsor his apprenticeship.

"There's no work," he said.

On Wednesday, as soon as he was released from the hospital, Farias returned to work.

"You can't let them scare you," he said.

Contact staff writer Jane M. Von Bergen at 215-854-2769 or jvonbergen@phillynews.com.