By Annemarie Evans
BBC News, Hong Kong
Oxfam is one of the biggest names in world aid and development
Notices attacking Oxfam Hong Kong as an organisation trying to infiltrate China have appeared on the websites of several universities in mainland China.
They appear to have been put there by China's Ministry of Education.
One of the notices called the development agency an illegal organisation with ulterior motives.
Oxfam staff have said they are puzzled by the accusations; China's Ministry of Education told the BBC it was investigating the issue.
Attributed to China's Ministry of Education, the notices tell students not to get involved in a training programme organised by Oxfam Hong Kong.
The notices claim that Oxfam's head is "a key member of the opposition camp". The head or heads being accused were not named.
The South China Morning Post newspaper in Hong Kong reported that the notice was written in the name of the ministry's Communist Party secretariat and asked students not to join Oxfam's training programme.
It was posted initially on the recruitment website of the Minzu University of China on 4 February.
Oxfam Hong Kong's director general, John Sayer, said the development agency was very surprised by the notices.
Oxfam trained young graduates to become programme officers for non-governmental organisations on the mainland, he said.
They had trained 40 graduates so far and there had never been a problem until now, he added.
"We've been doing it without any problems for four years, and with no indication from the government that there was any problem or it was in any way not suitable or sensitive in their eyes.
"And then suddenly we get this posting on the web telling the universities to back off and have nothing to do with us in regard to this programme," he said.
The students who take part receive a small payment per month, and most of the training takes place in impoverished western China.
It is part of Oxfam's wider poverty alleviation policy.