SALT LAKE CITY -- An exterminating company and one of its former employees pleaded not guilty Friday to allegations of unlawful use of a pesticide following the deaths of two young sisters.

Coleman Nocks pleaded not guilty to three counts each of misdemeanor unlawful use of a registered pesticide in U.S. District Court, and Bugman Pest and Lawn Inc.

President Ray Wilson entered the same plea to the same charges in a separate hearing.

Prosecutors contend Nocks disregarded the directions on the chemical's label and applied the rodent-killing poison Fumitoxin too close to a Layton home in February 2010. He and the company also didn't provide safety information about the pesticide to the home's residents, authorities said.

Investigators found toxic gas seeped inside, causing the deaths 4-year-old Rebecca Toone and her 15-month-old sister Rachel. The girls' parents and their two siblings, a brother and a sister, were also sickened.

The Utah medical examiner's office said the Toone sisters had elevated levels of phosphorous and lung damage "consistent with inhaling a harmful substance," according to information from Layton police.

U.S. Magistrate Judge Samuel Alba set a three-day trial for May 2.

If convicted on the class A misdemeanors, Nocks, 63, faces up to one year in federal prison and a $100,000 fine on each count. Bountiful-based Bugman Pest and Lawn faces a fine of up to $500,000 if the court decides the mishandling of the pesticides resulted in death.

Nocks was originally charged in state court with two counts of misdemeanor negligent homicide, but Davis County prosecutors dropped those charges because of the federal indictment.

After the hearing, Bugman Pest attorney Dennis James said the company has a long history of "strict adherence to safety procedures," including licensing compliance and careful training of its employees.

He said Bugman believes the record will show the incident at the Toone home was an aberration.

But records from state regulators show the company broke pesticide laws more than 3,500 times between April 2009 and February 2010. Some of the violations were related to poor record keeping, while others were related to the misuse of pesticides, including allegedly using too much Fuxmitoxin seven times over a period of 10 months.

Last summer, the company and seven of its employees, including Nocks, were fined more than $46,000 after investigation into the girls' deaths. Bugman was placed on two years' probation, which requires submitting to a records audit by the state agriculture department. Each employee also must attend 18 hours of pesticide applicator training.

Nocks voluntarily surrendered his applicator license and agreed never to reapply for license. He was not fined by the state.

Nocks has struggled emotionally with the deaths of the girls, said his federal public defender, Robert Steele.

"This is just horrible. ... He continues to be saddened by it," Steele said outside the Salt Lake City courthouse.