The Humane Society of the United States says it found "extreme animal abuse" and "deplorable conditions" at a Manheim egg farm owned by Kreider Farms.
The agency said Thursday that in February and March, an undercover investigator used a video camera to document birds severely overcrowded in cages, and dead chickens inside cages with hens laying eggs for human consumption.
Humane Society spokeswoman Anna West said the investigator also found birds with legs, wings and heads trapped in cage wires, among other problems.
"Flies caking the floors, ammonia levels that no human should be forced to work in, dead and dying birds basically mummified in these cages," West said.
Dave Andrews, a spokesman for Kreider Farms, said the allegations are not true.
"This video footage that they provided isn't even substantiated as to whether or not it's from one of our facilities," Andrews said. "I know this is part of their tactics, to shock people."
Andrews said the Humane Society is trying to scare people into supporting federal legislation that would provide much more space for hens and make other improvements at America's egg farms.
Kreider Farms President Ron Kreider said in a statement that the company has been tearing down old, traditional-style egg houses and replacing them with houses that have the larger, modern cages. He said more than 80 percent of their chickens are in the newer cages.