Alitalia had to cancel nearly two dozen flights on Monday due to a strike less than one week after it was restructured and relaunched under private ownership.The four-hour strike was called by the SDL union which represents flight attendants, ground workers and pilots. They were protesting against new work contracts and the criteria for laying off employees as the work-force was cut. The head of the union, Andrea Cavola, said: “The number of the workers is totally insufficient and has to be looked at again. The criteria used has to be revised; if things don’t change, this will be the first in a long series of strikes.” The airline’s problems with its strike-prone unions were one factor that repeatedly frustrated efforts to turn it around and make it profitable. The unions also blocked a take-over attempt by Air France-KLM which last week did buy a 25 percent stake in Alitalia.