WORCESTER— City police officers are set to vote today on whether to join a new union and leave the union that has represented them for many years.

The decertification election will be held from 2 to 5 p.m. at the police station at 9-11 Lincoln Square. It will be supervised by the state Department of Labor.

The election is the result of a petition brought in September by the New England Police Benevolent Association, a group that broke away two years ago from the International Brotherhood of Police Officers, which has represented Worcester patrol officers for three decades.

If the new union wins — by gaining more than half of the votes of the officers who cast ballots — it could signal a more militant bargaining stance by the rank-and-file officers, who have been working without a contract since the previous three-year pact expired in June.

The 364 members of the current union will face three choices on the ballot: stay with the current union; go with the rival union; or dissolve all union affiliation, a choice both unions oppose.

Officials from both unions have been lobbying hard in the days and weeks leading up to the vote.

The Lowell-based Police Benevolent Association held an open meeting last night at Maxwell Silverman’s restaurant, a few blocks from the station.

The meeting was the culmination of a week of intense campaigning by both sides that has included early-morning and afternoon leafleting of officers at the station, and meetings sponsored by the competing unions.

A potentially pivotal development in the contest occurred Monday when the local IBPO’s executive board voted 4-0 to endorse the rival union. The board members notified officers by e-mail Tuesday of their decision to recommend that voters drop the current union, said Detective Thomas G. Daly, secretary of the current union.

A key issue for the executive board, Detective Daly said, was the recent departure of the IBPO’s longtime lawyer, Richard K. Sullivan, who has handled contract negotiations and grievance and discipline issues.

Mr. Sullivan recently became affiliated with the Lowell law firm of Nolan, Perroni and Harrington, which works for the Police Benevolent Association.

“Richard Sullivan has 30 years of institutional knowledge. You can’t put a price on that,” Detective Daly said.

David E. Bernard, Massachusetts state director for the International Brotherhood of Police Officers, countered that Mr. Sullivan’s affiliation with the rival union’s law firm does not necessarily mean that police officers here will get his full attention.

“That doesn’t mean much,” he said. “Richard Sullivan’s name doesn’t appear on this ballot.”

Mr. Bernard also noted that several past presidents of his union’s Worcester local are endorsing the union and asking officers to vote for it to stay.

“This election is about the IBPO, the largest police union in New England and Massachusetts against a police group that’s been in existence for 18 months,” he said.

The New England Police Benevolent Association, which is part of the International Union of Police Associations, has 86 locals in Massachusetts and New Hampshire.

The International Brotherhood of Police Officers, based in Quincy, is under the umbrella of the National Association of Government Employees and the Service Employees International Union, which recently left the AFL-CIO to create the Change to Win labor federation. The union has affiliates and locals in eight other states and 90 locals in New England.