Norris, McLaughlin & Marcus is merging with a 37-lawyer Lehigh Valley litigation and commercial boutique, a move that gives the Somerville firm a presence in Pennsylvania and provides its new contingent — Tallman, Hudders & Sorrentino of Allentown — wider expertise to meet clients’ increasingly complex needs.

The merger is effective on Monday, and the addition of Tallman Hudders’ 24 partners, 11 associates and two counsel brings Norris McLaughlin to 151 lawyers in three offices — Somerville, New York and Allentown.