LA HABRA — Chuck Rizzuto is a union contractor who has no quarrels with anyone. But as a customer of the struck Owl Rock Product Co., he has become mired in its bitter fight with Local 12 of the Pasadena-based International Union of Operating Engineers.

On Tuesday night, vandals with ice picks broke into the La Habra construction yard of Rizzuto's Republic Concrete Inc. and punctured every tire of the 11 cars and trucks parked at the job site. On their way out, they sprayed-painted a warning message on a car: \o7 Owl Scab.\f7

La Habra police estimated the damage at $20,000.

The incident followed a string of similar vandalism carried out by unknown people on Republic's job sites in Riverside and San Bernardino counties in the past three weeks, Rizzuto said.

And Republic is not the only company that does business with Owl Rock to be struck by vandals. Similar incidents occurred recently in the yards of FST Sand and Gravel in Riverside, Gail Trucking Co. in Corona and other firms. Owl Rock officials estimated that recent vandalizing of Owl Rock job sites and of its customers and suppliers has totaled more than $500,000.

Owl Rock is one of Southern California's major suppliers of construction materials. Ontario-based Mitsubishi Cement Corp., a unit of Mitsubishi Corp. of Tokyo, bought a 50% stake in Owl Rock last year.

As with Rizzuto's firm, this is the first time vandals have broken into the FST job site, said Bill Medina, FST's general manager. And like Rizzuto, Medina was approached by union leaders weeks ago and told either to sever business ties with or find a non-union alternative to Owl Rock.

But customers remain unfazed. "The incident will not affect our relationship with Owl Rock, because their pricing is cheaper," said Medina, adding that Owl Rock does about $15,000 a month in business with his firm.

The troubles of Arcadia-based Owl Rock started five months ago, after its labor contract with the union expired. Negotiations on wages and benefits broke down in late September; the union went on strike.

The 26,000-member union represents workers at 20 Owl Rock plants in Los Angeles, Orange, Riverside and San Bernardino counties.

"We had vandalism, sabotage and picket-line violence from Sept. 29, the first day of the strike," said Mike Broome, Owl Rock's vice president of operations and assistant general manager.