Grassley sent a letter to Vilsack on Tuesday, asking whether the U.S. Department of Agriculture had received complaints and was what done to investigate the concerns. He also asked Vilsack whether there is a system in place for farm and USDA employees to report problems.
"The recent egg recalls ... have troubled consumers and weakened confidence in our nation's food supply," Grassley wrote in the letter. "When Americans visit their local grocery store, they should be able to trust that the food they are purchasing to feed their family is safe to consume."
The Iowa senator said his questions arose after two former workers at Wright County Egg near Galt, Iowa, claimed they complained about problems at the farm to USDA employees working there but were ignored.
USDA spokesman Caleb Weaver said Wednesday that the agency is working on a response to Grassley's letter.
Last week, Weaver said a USDA employee who oversaw agency operations at the farm did not recall any concerns being raised but the agency was continuing its investigation into the claims.
On Wednesday, Weaver said he did not have any additional information about the situation.
USDA employees at the farm inspect eggs and grade them but are not there to inspect for food safety issues. An agreement with the Food and Drug Administration does allow them to report unsanitary or other conditions that would require them to withhold the voluntary grading service.
The FDA has oversight of food safety issues, and a recent inspection by FDA investigators found rodents, maggots and leaking manure at Wright County Egg and Hillandale Farms of Iowa near New Hampton.
Those two farms recalled about 550 million eggs that were linked to about 1,400 illnesses nationwide.
About five weeks before the recall was announced, the FDA imposed new egg safety rules that call for increased monitoring and inspections at egg farms across the U.S.