Examples of wasteful spending given by the former employees ranged from leasing ordinary vehicles for $7000 a month to seeking embroidered towels at a cost of $7.50 each when ordinary ones would have cost about a third of the price.
The Texas company, which is already being examined by the military for possible overcharging for services, has consistently denied allegations of overbilling.
The two ex-employees, who contacted US Representative Henry Waxman, a Californian Democrat who has been critical of Halliburton, worked for the firm's procurement office in Kuwait.
Fuel and meals
Waxman and another Democrat Representative John Dingell of Michigan, wrote about the "whistle-blowers" in a letter to the Defense Contract Audit Agency (DCAA), which is already looking into whether one of Halliburton subsidiaries overcharged for fuel it took into Iraq and for meals served to US troops in the region.
"What is most disturbing about these allegations from the whistle-blowers is the regular and routine nature of the overcharging," the lawmakers wrote in the letter to the DCAA Director William Reed.
The DCAA confirmed receiving the letter and said it was under review.
Halliburton subsidiary Kellogg Brown and Root has a logistics contract with the US military that has so far received more than $3.7 billion in business, mostly in Iraq.
It also has contracts worth nearly $4 billion to rebuild Iraq's oil industry.
The massive contracts fuelled allegations that the White House was favouring Halliburton, once headed by Vice-President Dick Cheney.