A New York judge last week barred Robert F. Kennedy Jr. from appearing on the state’s November ballot, finding that the independent presidential candidate’s assertion that he had rented a bedroom in a friend’s home did not make him a New York resident as he had claimed.

On Monday, Mr. Kennedy’s opponents began trying to have him blocked a second time for good measure.

In a Mineola State Supreme Court courtroom, lawyers for two New York voters suing Mr. Kennedy’s campaign said that the campaign had employed a consulting firm whose subcontractors used deceptive tactics to gather signatures this spring to qualify him for the ballot. The plaintiffs, who are backed by the Democratic National Committee, want Justice Robert G. Bogle to order the State Board of Elections to keep Mr. Kennedy’s name off the ballot.

The trial, which is expected to last about a week, is likely to offer insight into the campaign’s expensive effort to secure ballot access in all 50 states. It could highlight the perils of hiring paid signature gatherers. And it could give Mr. Kennedy’s opponents a chance to erode his support in an election that could be swayed by mere thousands of votes.

On Monday, the plaintiffs’ lawyers argued that the nominating petition submitted by Mr. Kennedy’s campaign, which included about 150,000 signatures, had been riddled with errors and fraud.

The plaintiffs claim that canvassers misled New Yorkers into signing the petition to put Mr. Kennedy on the ballot. The New York Times reported in May that paid signature gatherers had been folding over the tops of petitions to conceal the names of Mr. Kennedy and his running mate, Nicole Shanahan, and that some had claimed they were gathering signatures for Democrats and generic third-party candidates.

In opening statements Monday, Thomas J. Garry, a lawyer for Elaine Portuondo Smith and Andrena Y. Wyatt, the plaintiffs, said that the candidate had been aware of the deception. After Mr. Kennedy learned about it, Mr. Garry said, he promised that the campaign would discard the signatures, but it did not.