And the answer is…when the biotech is controlled or affiliated with a privately run conglomerate. In this case, the US Department of Health & Human Services is likely to revoke a contract awarded last month to Siga Technologies, which is developing a drug to treat smallpox. The contract, perhaps worth as much as $2.8 billion, was part of a program that sets aside government work for small businesses.

The HHS’s Biomedical Advanced Research and Development Authority, or Barda, awarded Siga the contract to produce and sell 1.7 million treatments for the US Strategic National Stockpile. Barda has been criticized over preparedness for bioterror attacks and the contract was seen as an effort to reverse that concern. As noted in The Wall Street Journal, which first reported the story, no medicine is approved to treat smallpox, only a vaccine for prevention.

But the US Small Business Administration on Friday wrote Siga that the biotech doesn’t qualify as a small business because it “is controlled by and affiliated with” MacAndrews & Forbes Holdings, which is run by billionaire investor Ron Perelman. Siga’s rival, Chimerix, filed a complaint with the SBA, arguing Siga is “other than small” after HHS decided not to award contracts to both companies as the agency had indicated previously in order to prevent a monopoly situation.

“We believe it important that small businesses be able to compete on an equal footing for government contracts designated as set-asides,” says Chimerix ceo Ken Moch, in a statement. “We have made every effort to work closely with Barda to ensure this procurement was conducted both expeditiously and within the parameters of the law.”

In a statement, Siga ceo Eric Rose says Siga will file an appeal.