Mayor Bloomberg wants to eliminate all party primaries from New York City elections. To accomplish this he appointed a Charter Revision Commission to place a referendum question on this November’s ballot. That referendum question marks a misguided effort to repeal one of the greatest reform measures of the 20th century: allowing people to directly elect their party’s nominee through primaries.

In New York, party primaries have long been our way to ensure that voters choose their party’s candidate for mayor, public advocate, comptroller, borough president and City Council.

Yet, if Mayor Bloomberg gets his way, more than three million New Yorkers who have chosen to register with a political party, rather than leave their political affiliation blank, will no longer be able to help elect their party’s nominee.

Why is the mayor calling for the elimination of party primaries?

Those who favor the elimination of party primaries say it will “open the doors” of our election system. But those doors are already wide open to anyone who wants to participate.

Just think of what we’ve accomplished under our current election system: New York City has elected its first African-American mayor and comptroller, and female borough presidents. New York City has also elected its first Dominican, Caribbean-American and Asian-American City Council members.

And in recent years we’ve made changes to our election system that have produced many positive results. These changes include strengthening the city’s landmark campaign finance program, implementing term limits, and easing some of the ballot access rules that apply to candidates who run for office.

In 2001, when the term limits law kicked in and the campaign finance program’s four-to-one matching funds law first took hold, nearly 250 candidates ran for office. Those candidates represented fresh political voices who engaged voters in dynamic primary campaigns that energized the city.

Our current election system continues to produce a large and diverse field of candidates running for office. This system also gives voters clear choices and has successfully elected city leaders from both parties. There is no need to dismantle our current election system, especially when one takes into account the unintended consequences associated with the mayor’s initiative.

Among those unintended consequences is the possible weakening of the city’s campaign finance program. In fact, Bloomberg’s proposal could make it easier for millionaires and billionaires to run for office and win. And some even say that the elimination of party primaries could strengthen the party leadership, or so-called party bosses, at the expense of rank and file party members.

Like doctors who operate under the directive to “first, do no harm,” those dealing with electoral laws should be equally careful. Indeed, electoral reforms are famous for having undesirable consequences. Mayor Bloomberg’s initiative to eliminate all party primaries is no different.

New Yorkers know that political parties, which have brought hundreds of thousands of New Yorkers into the political process, help democracy thrive. That’s why political parties and party primaries must continue to play a critical role in our city, state and nation.

This November, I urge New Yorkers to reject Mayor Bloomberg’s initiative to dismantle our current election system by eliminating party primaries in New York City.

Denny Farrell, Jr. is chairman of the New York State Democratic Committee.