A Thai official denied the allegation.
Twelve loggers were shot dead on March 5 - followed by three more a week later - after entering Thailand from Cambodia's northern province of Preah Vihear to cut rosewood, Cambodian military intelligence officer Preap Thoeurth said by telephone.
"Authorities have educated the people not to cross the border to log, but rosewood is very expensive," he said.
Pen Song, a Cambodian military commander in the province, confirmed the incidents.
"We have asked them (the Thai military) not to kill Cambodian loggers, but to arrest them or to fine them, but they still keep killing. We don't know what to do," he said.
But Maj Gen Prawit Hookaew, a regional spokesman for the Thai army, rejected the accusation, saying it was "impossible" for so many Cambodians to have been killed without a formal protest by Phnom Penh.
Cambodian loggers are routinely caught sneaking into Thailand, often in search of rosewood, which fetches thousands of dollars per cubic metre and is in strong demand in China and Vietnam.
Years of rampant illegal felling in Cambodia have devastated the country's own luxury timber stocks.
Cambodian officials, including Prime Minister Hun Sen, have repeatedly urged Thailand to arrest trespassers instead of firing at them.
The border between the two countries has never been fully demarcated, in part because it is littered with landmines left over from decades of war in Cambodia.
Thai forces allegedly shot dead at least 69 Cambodian loggers last year for illegally crossing the border, according to information released by Cambodia's interior ministry last month.