(Reuters) - American Airlines Group Inc AAL.O shares plunged on Friday after the company's release of its fourth-quarter and full-year 2016 results, as mounting costs and growing wage pressures spooked investors.

An American Airlines airplane prepares to land at the Jose Marti International Airport in Havana September 19, 2015. REUTERS/Carlos Garcia Rawlins

Following the Fort Worth, Texas-based carrier’s pre-market disclosure of its 2016 performance, prices had briefly spiked, as American met analyst forecasts and outperformed its peers on unit revenue.

They quickly reversed course, however, after a conference call with company executives, industry analysts and members of the media, where discussions of increasing labor costs pushed stock prices down 4.84 percent to $47.19 in midday trading.

“After the call, I think it was mainly a discussion of costs that derailed their stocks,” CFRA Research analyst Jim Corridore said in a phone interview. “There’s huge wage pressures going on, not just for American but for the whole group.”

Across the industry, airlines in recent years have begun to recover from several turbulent years of unprofitability. Labor unions in turn have demanded a more even disbursement of wealth after years of wage austerity that curbed significant pay increases.

American’s labor costs are rising partly due to a 2015 agreement, reached with its pilots, that included a substantial pay bump.

Still, American, the No. 1 U.S. airline by passenger traffic, posted positive results in unit revenue, which reflects sales relative to flight capacity, noting a 0.2 percent increase in the metric. Its biggest U.S. rivals have not expected to see positive growth until the first quarter of 2017.

Positive changes in unit revenue are a welcomed sign for investors as the industry has for years been battered by cheaper fares and increased competition.

American’s largest U.S. rival, Delta, noted a 2.7 percent decline in the same measure for its fourth quarter 2016 and said it expected a flat to 2 percent increase in the first quarter of 2017.

American met analyst expectations on fourth-quarter earnings per share at 92 cents per share, according to the average found on Thomson Reuters I/B/E/S.

The company reported a net income drop to $289 million, or 56 cents per share, in the fourth quarter ended Dec. 31, from $3.28 billion, or $5.09 per share, a year earlier, when it recorded a $3 billion tax benefit.