NORTHAMPTON — Cooley Dickinson Hospital , its parent Mass General Brigham and the Massachusetts Nurses Association have reached a tentative agreement on a new three-year contract.

The deal, reached Friday and announced Tuesday morning, avoids the need for a one-day strike already authorized by the nurses.

The deal includes pay increases, according to the union, and an across-the-board increase of more than 8.5% for all grades in year one, retroactive to April 1. That will be followed by a 2.5% across-the-board increase in year two; followed by a 3% across-the-board increase in year three; and a 2% lump sum for nurses at top step in years two and three on job anniversary dates.

The across-the-board increases are in addition to annual step scale increases nurses receive, according to

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