A construction strike affecting projects in nine counties, including a massive overhaul of the Dan Ryan Expressway, began at midnight.

Negotiations between the laborers' union and negotiators for area contractors began May 1 but broke off late Tuesday, according to a statement Wednesday from the Construction and General Laborers' District Council of Chicago Vicinity.

The remaining issues between the construction workers and the Mid-America Regional Bargaining Association included pension fund guarantees, subcontracting protections and other "economic issues," according to the statement.

The contractors offered to increase wages 5.3 percent over each of the next two years and leave current pension and welfare benefits intact, MARBA said in a release. The workers' current base wage rate is $30.15 an hour.

The strike affects projects in Boone, Cook, DuPage, Grundy, Kane, Kendall, Lake, McHenry and Will counties. MARBA represents more than 200 construction companies, or about 10 percent of the construction market, the union said.

The sides have not scheduled any future meetings. The laborers will continue to negotiate with independent contractors and other construction employer groups, the union said.

"We're ready to sit down and talk whenever they are," said Randy Larson, negotiation coordinator for MARBA.

The two-year, $600 million Dan Ryan Expressway construction project is the largest highway rehabilitation in Chicago's history. Traffic planners hope the changes will reduce chronic congestion on a road that handles 320,000 vehicles a day.