Suffolk County National Bank’s holding company has been sued by a shareholder seeking to block its merger with a Connecticut bank company.

Riverhead-based Suffolk Bancorp improperly favored People’s United Financial Inc. over other suitors when it agreed to be acquired by the Bridgeport, Connecticut-based company, the plaintiff, Paul Parshall, charged in the lawsuit, filed Thursday in federal court in Brooklyn.

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The all-stock, $402 million transaction awaits approval from regulators and Suffolk Bancorp shareholders.

Suffolk Bancorp declined to comment on the lawsuit, a company representative said Monday. The company has 27 branches on Long Island and in Queens.

The lawsuit, which is seeking class action status, named Suffolk Bancorp, as well as its chief executive, Howard Bluver, its directors, and People’s United, the holding company for People’s United Bank N.A.

Citing a sequence of events spelled out in Suffolk Bancorp’s securities filings, the suit charged that Bluver “steered the deal” to People’s United in order “to secure employment with the combined company,” and that the defendants made “misleading” statements in support of the transaction.