"There are big cost implications for both contractors and the labor force," says one union official who did not want to be identified.

He says labor agreements with trade unions require builders to guarantee workers a 40-hour work week, which means a regular weekly pay for workers pulled off a job. Even laborers working without contracts will feel the pinch as builders pare down their workforce through layoffs, he says. Add to that the cost incurred to rent earthmovers and other construction equipment and the delay could send costs skyrocketing, he says.

Menino called for an end to construction work along the Rose Fitzgerald Kennedy Greenway earlier this week after a 12-ton slab of concrete fell from a tunnel roof, crushing a car and killing 38-year-old Milena Del Valle. The disaster sparked an expansive federal and state probe into the state's oversight of the construction and the companies responsible for managing, designing and building the $14.6-billion project, known as the Big Dig.

City officials were unable to say how many construction projects were halted as a result of Menino's request but a source familiar with the shutdown said it will have "a major impact" on the budgets of developers involved in construction projects along the Greenway. It was unclear how long the work stoppage would last but officials say it could be weeks--or longer--before defects to the underground network of Big Dig tunnels are identified and repaired.

The mayor ordered contractors to stop street repairs several weeks ago after he became concerned over the way potholes were being repaired in the city, says the source. That stoppage, which lasted for about a week, cost contractors several hundred thousand dollars before the mayor met with the contractors to discuss his concerns.