Delta Air Lines and Northwest Airlines agreed late Monday to merge, in a $3.1 billion deal that would create the world’s biggest airline and could prompt other airlines to pursue mergers of their own, the New York Times reported today. Another leading merger candidate is a combination of United Airlines and Continental Airlines, which have explored the idea. The airlines now may try to get the deal wrapped up within the next 30 days. The Delta-Northwest agreement came despite failed efforts to get pilots at both airlines to agree on how to combine their own ranks, an issue that could lead to labor unrest and disruptions to flight operations in the coming years. Northwest pilots immediately said that they would oppose the deal.

In a sign that merger talks with Northwest Airlines Corp. have stalled, top executives of Delta Air Lines Inc. issued a memo to employees saying that no “potential transaction meets all our principles,” the Wall Street Journal reported today. The memo comes as executives at the two airlines wait for their pilots to reach an accord among themselves on seniority — an accord needed before a merger can move forward. In its memo, issued yesterday, Delta said that seniority for all its employees is one priority it would consider in any merger. Delta also cited other priorities, such as keeping its Atlanta headquarters. It added the airline will continue to focus on its “stand-alone plan” until all “these conditions are met.”