Mississippi-based Cal-Maine Foods, the country’s largest egg producer, has disclosed that the federal government is investigating the company regarding recent egg price increases.

Shares of Cal-Maine Foods, the largest U.S. egg producer, fell more than 4% in after-hours trading Tuesday after the Ridgeland, Mississippi-based company said it received notice of the probe last month regarding egg price increases and that it is cooperating with authorities.

Egg prices have soared in recent months, driven by a bird flu outbreak that led farmers to cull over 166 million birds, primarily egg-laying hens. In February, a dozen Grade A eggs averaged $5.90 in U.S. cities, up 10.4% from a year earlier and surpassing January’s record-high $4.95.

Cal-Maine, which supplies about 20% of the nation’s eggs, has faced growing scrutiny. On Tuesday, the company reported fiscal third-quarter sales of $1.42 billion, nearly double the previous year’s figure, largely due to higher egg prices. The average price per dozen jumped from $2.25 to $4.06. However, sales fell short of Wall Street’s $1.43 billion estimate.

The company sold a record 331.4 million dozen eggs in the quarter, up 10% from the prior year. It also reported progress in mitigating bird flu’s impact by increasing the number of layer hens and chicks hatched and recovering from facility closures in Texas and Kansas. Lower feed costs also helped.

Net income more than tripled to $508.5 million, or $10.38 per share, though it fell below analysts’ expectations of $10.72 per share.