The UNHCR says that Montagnard refugees are now making their way directly from Vietnam's Central Highlands to the Cambodian capital, Phnom Penh.
The refugees are asking the UNHCR to help them recover tribal lands, and many are refusing an offer of resettlement in the United States.
The Montagnards had until recently been making their way to UNHCR facilities in the border province of Ratanakiri.
Now they are heading directly to Cambodia's capital.
This presents two problems for the UNHCR. There is a lack of accommodation in Phnom Penh. And it is more difficult for them to persuade the refugees to return to Vietnam.
The Montagnards are members of ethnic minority groups in Vietnam's Central Highlands.
They claim their tribal lands have been taken to grow cash crops and that they face constant harassment from the police.
Since the middle of the year, a steady trickle of refugees have come over the border.
Recently the numbers have increased and there are now almost 600 Montagnards in Cambodia.
Some of the refugees have accepted an offer of resettlement in the United States. Others want the UNHCR to intervene in their land dispute. But the UNHCR say they cannot interfere with internal affairs in Vietnam.
In the refugee facilities, there has been tension between Montagnards who have decided to go to the US and those who want to stay in Cambodia.
The Cambodian government insists they will not allow the refugees to remain in the long term.