Kansas City, Mo. ? A federal judge has threatened to ignore sentencing guidelines and give an Independence man a much longer prison term for a federal gun conviction unless he provides information about his missing children.

Daniel Porter, who pleaded guilty in January to one count of being a felon in possession of a firearm, is accused of kidnapping his two children after he picked them up from his estranged wife on June 5 for a weekend visit.

The children, Samuel, 7, and Lindsey, 8, have been missing since then, and Porter has refused to disclose their whereabouts.

The case has gained national attention, and on Wednesday Jackson County Prosecutor Michael Sanders and the children’s mother, Tina Porter of Independence, appeared on the “Dr. Phil” television talk show to drum up publicity for their search.

Investigators have scoured the Kansas City suburbs of Independence and Sugar Creek looking for the children, and they have searched in the area around Porter’s hometown of Trenton in northern Missouri. He is facing a charge in Jackson County of two counts of parental kidnapping.

“The court will consider whether a … reduction for acceptance of responsibility is appropriate in light of defendant’s refusal to reveal information concerning the whereabouts of the missing children,” U.S. District Judge Ortrie Smith wrote.

Federal sentencing guidelines call for a prison term of two years and nine months to three years and five months for the gun conviction, but Smith filed a brief Thursday saying he might not give Porter credit for pleading guilty to the crime.

Porter could face up to 10 years in prison and a $250,000 fine. Smith’s order put Porter on notice that he should not expect to receive a lesser sentence.

The U.S. Supreme Court recently ruled that sentencing guidelines are “advisory,” meaning judges have the discretion to sentence criminals to the statutory maximum if the sentence can be shown to be “reasonable.”

“There is a lot of pressure brought to bear on Dan,” Sanders said. “We hope that the pressure will make him do the right thing.”