Senator Christopher Dodd in a letter to Defence Secretary Donald Rumsfeld on Wednesday asked for details on the Pentagon's progress in setting up the reimbursement programme and questioned why it was not in place yet.
"Very simply, this is either negligence on their part, because they were not happy with this when it passed, or it's incompetence," Dodd said.
"It's pretty outrageous when you have all their rhetoric about how much we care about our people in uniform."
The Pentagon had no immediate comment.
Soldiers serving in Iraq and their families have reported buying everything from higher-quality protective gear to armour for their Humvee vehicles, medical supplies and even global positioning devices.
In response to the complaints, Congress last year passed Dodd's amendment requiring the Pentagon to reimburse members of the Armed Services for the cost of any safety or health equipment that they bought or someone else bought on their behalf.
Under the law, the Defence Department had until 25 February to develop regulations on the reimbursement, which is limited to $1,100 per item.
"Very simply, this is either negligence on their part, because they were not happy with this when it passed, or it's incompetence"
Senator Christopher Dodd
Dodd asked that Rumsfeld provide details on the department's progress. But he also said it was unclear what recourse he has, other than public embarrassment, to force the Defence Department to act.
Senator John Kerry, who repeatedly decried the lack of equipment during his unsuccessful presidential campaign, said the Pentagon needed to move quickly to give the troops their reimbursement and armoured Humvees.
"They should be living up to the letter of the law," Kerry said.