So far, seven MPs from the Cambodia National Rescue Party (CNRP) have been picked up.
A party activist has also been detained.
If convicted, they face up to 30 years' jail.
The arrests came after an opposition-led rally in the capital Phnom Penh earlier this week turned violent.
Dozens of people were hurt, some of them seriously.
Presenter: Sen Lam
Speaker: Yim Sovann, CNRP spokesman and member of parliament
SOVANN: So far, the administration controlled by the CPP (Cambodian People's Party) has arrested 7 member of parliament-elect from from CNRP. The arrest is definitely related to the political stalemate between the CNRP and the CPP. The arrests are politically motivated. This is a threat and intimidation to MP-elect from the CNRP and leaders of the CNRP. We condemn the violence, provoked by the security personnel controlled by the CPP. They are the one who provokes violence. Since 6 months, since January 2014, a lot of violence occur by the security personnel controlled by the CPP. We cannot tolerate this. This is against the Constitution, against the law and against the democratic principles.
LAM: And Yim Sovann, as far as you know, are all those people still in detention or have some of them been released?
SOVANN: Yes, they are still in pre-trial detention and I don't know how many more will be arrested. We follow up the situation very closely today.
LAM: And what your own position, do you fear for your own safety, do you think they might arrest you?
SOVANN: No. I am not, I did nothing wrong. I not fear for my own safety, but I fear for the safety of the whole nation. I fear for the life of democracy, I now, I think that the democracy in jeopardise, that is why the international community should come and help Cambodia. Now, you can see that Surya Subedi, UN envoy in charge of human rights in Cambodia already expressed this opinion that if there is no solution to the political stalemate, no reform, in the election, there will be instability, there will be violence in the future. So we try our best to avoid violence. We want to respect the principle of non-violence, that is why we want the CPP come to table, to negotiate peacefully, to find a solution in order to end the political stalemate.
LAM: And Yim Sovann, you spoke of the international community. Will you be approaching donor countries, like Australia, to pressure the Hun Sen government over those arrests?
SOVANN: I think just not only Australia, but Japan, the Europeans, United States. We have approached them in the last few days and I believe that they will help, they will compromise, to find a solution, to the political stalemate.