It took a year of wrangling with the European Commission for Germany's Lufthansa to gain approval to buy 41% of Italy's ITA Airways, and only after it accepted big concessions.
While the deal expands Lufthansa's footprint in the lucrative southern European market, the combined group will have to cede some routes and slots to rivals for it to proceed.
Industry executives, investors and experts say greater scrutiny of such tie-ups by European regulators and demands for remedies could deter major airlines from further deals.