Holding hard hats high to salute helmets on empty chairs in St. Patrick’s Cathedral, thousands of city construction workers yesterday paid tribute to their colleagues killed in a growing number of deadly accidents this year.

Construction workers held an unprecedented Mass to remember fallen workers, joined by the families of victims in a March crane collapse and several other high-profile accidents in the city. Many came straight from construction sites in work boots and jeans after several contractors closed down jobs early.

Bells rang as labor officials recited the names of 26 union and nonunion laborers who died in the city in the past year. The dead include six of seven victims of the March 15 crane collapse, a window washer who fell off a Manhattan skyscraper, and a man who plunged 40 stories to his death off a Donald Trump tower.

“They didn’t die in vain,” Father Brian Jordan, who served as a chaplain at ground zero, said. “They upheld the dignity of human labor.”

The ceremony was on Workers Memorial Day, which is held annually to commemorate the 1970 Occupational Safety and Health Act. But city construction workers have not held a Mass this large before and many said the crane collapse called greater attention to the high risks of their industry.

“I went to three funerals in a week” after the collapse, a senior superintendent at Bovis Lend Lease, Ralph DiDonato, said. “Construction workers are the tightest crew when it comes for caring for people.”

The number of deaths cited at the service does not match the city Buildings Department, which also lists non-construction worker deaths and has said fewer people have died: 13 this year, 12 last year.

Organizers couldn’t immediately explain the discrepancy, although federal agencies compile different data for construction-related deaths, sometimes using criteria that include a wider range of projects.

The city’s buildings commissioner resigned last week, days after disclosing at a hearing that the building under construction before the crane collapse had improperly received construction permits. The city’s acting commissioner, who attended yesterday’s service, ordered a review of high-risk construction practices, including crane and concrete pouring operations.

Several times the workers raised their hats to nine empty chairs, each with a different colored hard hat and roses or daffodils on the seats. Eight referred to the union construction workers who lost their lives in the past year, while the ninth represented the 18 who died in nonunion jobs, Father Jordan said.