Alitalia's 62 years as a state-run firm ended in bankruptcy
Strike action has forced the newly-privatised Alitalia to cancel flights less than a week after its relaunch.
The Italian airline said it had cancelled 22 flights due to a four-hour strike, which began at 0900 GMT.
The walkout was called to protest against new contracts and hiring policies at the new Italian carrier.
Alitalia has been taken over by a group of prominent Italian business leaders which formed an alliance with Air France-KLM.
Unofficial protests at Rome and Milan airports marred the launch of the new Alitalia last Tuesday, causing some delays and cancellations, but Monday's strike is the first official walkout of the new era.
The SDL union has said it may call a further 24-hour strike at an unspecified date.
The new Alitalia has set more modest targets than the old one, with its 148 planes making 670 flights daily and serving 70 national and international destinations.
The carrier is slimmer than its predecessor, with about 12,500 employees, down from more than 23,500 between the two airlines before the merger and relaunch.
Alitalia's 62 years as a state-run company ended in bankruptcy, due to falling sales, frequent strikes and an oversized workforce.
The new Alitalia is a private company owned by a group of Italian investors who have merged much of the old carrier's profitable assets with the much smaller Air One.
Air France-KLM, whose attempt to take over Alitalia was thwarted by union opposition, has a 25% stake.