(Reuters) - Tyson Foods Inc disclosed on Monday it has received a subpoena from the U.S. Securities and Exchange Commission following allegations it conspired with rivals for years to fix chicken prices.

Tyson food meat products are shown in this photo illustration in Encinitas, California May 29, 2014. REUTERS/Mike Blake

The chicken sector, which is dominated by a handful of large meat companies, has come under increased scrutiny over the past year as customers and farmers have alleged antitrust violations relating to pricing, production and compensation.

U.S. poultry buyers claimed in a lawsuit in 2016 that Tyson, the nation’s biggest chicken processor, and its competitors had colluded since 2008 to reduce output and manipulate prices.

Tyson, Pilgrim’s Pride Corp and Sanderson Farms Inc have denied the accusations.

Investors in separate lawsuits have alleged the processors made misleading statements or failed to disclose information about price fixing.

Tyson Chief Executive Tom Hayes declined to share details about its subpoena on a conference call with reporters after the company reported better-than-expected quarterly sales and profit. He said the company had not changed pricing practices.

Tyson received the subpoena from the SEC on Jan. 20 in connection with an investigation related to the company, according to regulatory documents.

The seller of Ball Park hot dogs said it had limited information and was cooperating with the probe, which is in an early stage.

Pilgrim’s Pride said it had not received a subpoena from the SEC. Sanderson Farms declined to comment.

Tyson’s stock ended down 3.5 percent at $63.13. Shares of Pilgrim’s Pride, mostly owned by meat packer JBS SA, lost 4 percent to $18.64. Sanderson Farms shares slid 1.9 percent to $89.50.

Commenting on the subpoena, JPMorgan analyst Ken Goldman said “obviously it is not a positive” for Tyson.

Joe Agnese, analyst for CFRA Research, said the news will restrict Tyson’s valuation until investors’ concerns are alleviated.

The subpoena arrived as Hayes is finding his footing as Tyson’s new CEO after taking over for Donnie Smith on Dec. 31.

Tyson has sought to increase profit by selling more value-added items such as pre-seasoned products and heat-and-serve meals, which command higher margins than basic meats.

Net income attributable to the company rose to $1.59 per share in the quarter ended Dec. 31 from $1.15 a year earlier. Sales were $9.18 billion, up from $9.15 billion.

Analysts on average expected earnings of $1.26 and revenue of $9.05 billion, according to Thomson Reuters I/B/E/S.

Tyson raised its full-year profit forecast to $4.90 to $5.05 per share from $4.70 to $4.85.