PHILADELPHIA (CBS) — The union representing heavy equipment operators has called a strike against the General Building Contractors Association.

Members of Operating Engineers Local 542 were told to go home early Tuesday morning after arriving at job sites throughout the region.

In Center City, the Comcast Center served as ground zero, with shop stewards getting the word out while members of other trades waited to hear if they should stay off the job as well.

Some did as iron workers and glaziers cited safety concerns.

Nevertheless, this strike does not feature a picket line.

“We didn’t want to hurt the other crafts so we just pulled our guys off the job,” said 542 Business Manager Robert Heenan.

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He says the decision to strike was the result of nearly four months of futile negotiations with the Contractors Association.

The job action involves operators of cranes, bulldozers, hoists and all kinds of other heavy equipment.

It could throw many construction projects off schedule, depending on the length of the strike, and no new talks are scheduled.