After talks to end a three-day construction slowdown failed Thursday, the union representing crane and backhoe operators said it will protest at the new Comcast tower construction site Friday morning, starting as early as 6 a.m. No new talks are scheduled. The union's contract expired April 30.

At odds are the General Building Contractors Association and Local 542 of the International Union of Operating Engineers. Core compensation is not the issue — both sides have agreed on a $2 an hour wage increase across the length of the contract.

The dispute centers on overtime rates on the weekend, the use of apprentice oilers and how a marketing fee to fund the GBCA would be collected. The union also says that the subcontractors who employ them are at the bargaining table, but are unable to make a decision without consulting with general contractors.

Hundreds of heavy machinery operators are not working, but the union has not set up a picket line that the other unions would be reluctant to cross. As a result, construction has slowed, but not entirely stopped, at about 30 job sites across Philadelphia and the region, including the Philadelphia Museum of Art, East Market, the Comcast tower, Chester County Hospital, and the Aloft Hotel.

Practically speaking, construction will eventually come to a halt because the crane operators hoist heavy materials such as beams and run construction elevators that move materials and people from floor to floor.