First Niagara Financial Group said it would cut about 4 percent of NewAlliance Bancshares’ workforce as part of its $1.5 billion takeover of the New Haven-based lender.

New York-based First Niagara plans a net reduction of 50 positions in 2011.

While 230 back-office and support positions are expected to be affected, 180 new customer-facing positions will be created in the New England region, First Niagara said.

However, the job cuts will not impact any branch positions and all 88 NewAlliance locations will remain open after the merger, it said in a statement.

In September, Connecticut began to probe First Niagara’s takeover of NewAlliance, throwing up a potential roadblock before what was then the nation’s largest bank deal in nearly two years.

First Niagara and NewAlliance shares were largely unchanged Monday afternoon on Nasdaq and the New York Stock Exchange, respectively. First Niagara shares were trading at $13.70 while those of NewAlliance were trading at $14.47.

Shares of First Niagara have gained 7 percent after the takeover was announced in August. NewAlliance shares have rallied 27 percent in the same period.