A garbage carting union responsible for collecting about a third of New York’s commercial refuse walked off the job early yesterday morning, raising fears the city could become ensnared in another pungent strike.

Members of Local 813 of the Teamsters Union said the company, Waste Management Incorporated, insisted that workers pay part of their health care premiums, lose time and a half pay for work on Saturdays, and forgo other key clauses from the previous contract, which expired on November 30, 2005.

The likelihood of garbage piling dangerously high on the city’s streets is low, however, as replacement workers brought in by the Houston-based company to continue operations began work yesterday. Waste Management has about 10,000 commercial customers in New York.

The two sides negotiated with the help of a federal mediator until just before the transit workers went on strike in late December. Company negotiators made their final offer on December 18, but the 123 members unanimously voted against the contract, the president of the local union, Sylvester Needham, said.

The union then voted to strike, but delayed action because the transit union was already snarling the city, Mr. Needham said. The company then unilaterally imposed its proposal, which included a 3% pay raise.

The union made a last-minute offer on Friday, proposing that workers begin paying a portion of their health care premiums on the 25th month of a new contract, but the company rejected the offer. “Our goal in the talks is to reach a fair and equitable agreement,” a spokesman for Waste Management, George McGrath, said.

A garbage carter from the Bronx who works an average of 56 hours a week, Stanley Mitchell, estimated he would make between $6,000 and $7,000 less a year due to lost overtime pay and health care payments. He said the company’s proposed contract was not affordable for his family.

Health care benefits are especially important for garbage carters because of the hazards of the job, Mr. Needham said. Workers have been pierced by hypodermic needles, cut by glass, and pinched by metal, he said.

About 100 workers from Local 639 of the Teamsters Union in Washington, D.C., also went on strike yesterday, after employers at the local branch of Waste Management tried to force a similar contract, members said.

Mr. Needham said the union might have to escalate the strike. “We’re not going to just sit here with our hands in our pockets,” he said. “There’s a lot of things we can do to put pressure on the company.” Mayor Bloomberg said that if garbage goes uncollected, the city would declare a health emergency and use Department of Sanitation resources to pick up the trash.