Thai academics are well-known voices on television and radio as analysts and commentators providing lively debate on politics. But broadcasting freely is no longer a simple and safe matter since the government crackdown against Red Shirt protesters in May.

Many radio stations where academics have spoken in support of anti-government Red Shirt demonstrators have been shut down and academics warned by their own universities against openly broadcasting their opinions.

Regular commentators on mainstream radio and television stations have also become more cautious although the change is sometimes subtle: "Many professors are reluctant to take sides, often they censor themselves. If I talk about linguistics I have to be [politically] neutral," said Suda Rangkupan (pictured), a lecturer in linguistics at Bangkok's Chulalongkorn University.

Suda has considerably reduced her broadcast appearances. Her reluctance and that of her colleagues has tended to strangle open debate given that Thai academics appear on broadcast media far more than in most other countries.

"Many academics have a show on mainstream radio, especially the law and politics professors who are famous. They may be interviewed every week, once or twice a week," she said.

Ominously, the warnings are not just from the government. Last month, at least one major university distributed a circular saying professors should not be "openly involved in political conflict".

Prestigious Chulalongkorn University in the heart of Bangkok sought to distance itself from comments made by its academics. In a letter, the university said they should not refer to their university affiliation when commenting on broadcast media or in interviews.

"We are not allowed to say we are from Chulalongkorn. The university authorities believe people will be convinced by what we say because we have respect in society as academics of this university," Suda said.

Universities in Bangkok in particular have become nervous about political involvement. "There has been more pressure on the faculty not to be involved in any [political] movement even though they have been involved for years already," she said.

"The reason I joined the Red Shirts is that it is a movement for democracy. I believe it should not be a problem. I've spent the time after work. It's nothing to do with the job. In the second week of June I found in my mailbox an official note from the head asking for cooperation from every faculty member not to talk about politics in classes and not to encourage students to join the movement."

Suda had her own shows on community radio stations which have been targeted by the government in the wake of the bloody crackdown in May.

The stations have a broadcast radius of just five kilometres. First launched around five years ago, they have become popular and some broadcast from university campuses.

One station, Taxi Radio, was created by a group of taxi drivers and aired Suda's programme on Saturdays. Another of her shows, 'Thai Voice', was broadcast on Sundays from the outskirts of Bangkok on a station called Thais Love Thais.

"It is radio for the people. It is grassroots people who listen," said Suda. "I try to explain to them what is going on in this country."

Suda had used the first hour of her two-hour Sunday show to translate English-language news despatches into Thai, then left 45-60 minutes for listeners to call in.

"When Thai newspapers quote English-language newspapers they distort the news. I explained to my listeners that Thai newspapers don't give the right translations," said Suda.

"The listeners called in and talked about how they feel about politics. It gave them a chance to express themselves. Some of the taxi drivers would stop their cars on the way and give us a call. Sometimes they wrote a poem and read it on air."

"Many of the listeners don't have very good English. They don't have the internet. Most are of the lower classes - market vendors, motorcycle and taxi drivers, and usually they are independent, not office workers. Most of them are Red Shirt supporters.

Between 7 and 10 April most radio stations were shut by the authorities and the closures have accelerated since the 19 May crackdown. Radio stations that supported the Red Shirt movement have gone, including the two that broadcast Suda's programmes.

"I met the DJs I used to work with at a temple one month after the bloody crackdown, to remember the dead. They said even the radio transmitters had been removed," she said.

Taxi Radio was jammed as early as April before it was shut down by its owner Chinawat Haboonpak, a Red Shirt activist. "There are 5,000 to 6,000 [community radio] stations but they won't allow even one [Red Shirt] station to exist," Chinawat said.

Some reported soldiers had raided broadcast stations and damaged equipment in the aftermath of the May crackdown.

The government has said such radio stations have divided society, "spread lies" and urged people to commit violent acts during the protests that wracked Bangkok in April and May.

Staff of the Red Shirt We Love Udon radio station were arrested in May and the station chief has been charged with terrorism.

Government spokesman Panitan Wattanayagorn described Red Shirt broadcasters as a "threat to national security". But Suda said only the radio stations that supported the democracy movements were closed whereas those run by the pro-government Yellow Shirts were still open even though they were also community radio stations.

"It was very difficult for the government to let these community radio stations continue. They feared if they let us have a radio we can use it for communications, to talk and discuss and use for political purposes and they will be believed as an accurate source of media because mainstream media are always self-censored."

Meanwhile, the Bangkok Post newspaper reported that more than 100,000 websites and blogs, many by academics, had been blocked, some of them simply for mentioning the name of Red Shirt academic Giles Ji Ungpakorn.

The number of people willing to speak out is dwindling by the day. Suda recently received a note from her university head of department pointing out that her subject, linguistics, had nothing to do with politics.

"It is our duty as academics to help the people understand the issues, but I have decided not to show up [on media] as an academic any more. I am just a Thai person," said Suda.