Construction has begun on Portside at Pier One, a long-delayed mixed-use development on the East Boston Waterfront, the developer’s parent company said.

A spokeswoman for Mack-Cali Realty Corp. said that the firm’s Roseland subsidiary had begun work in December on the first phase of Portside, a $67 million luxury apartment complex. The five-story structure will include 150 market-rate and 26 affordable apartments.

The developer will host an official groundbreaking ceremony Monday. Mayor Thomas M. Menino has declared the revitalization of the East Boston Waterfront a priority for his administration.