A new law makes criticism of the Constitutional Court punishable by imprisonment, giving extra protection to a body that in recent years has made controversial rulings altering the shape of governments.

The unheralded 31-page law took effect when it was published last week in the Royal Gazette.

It says "honest" criticism without "rude, sarcastic or threatening" words is not in violation of the law, but if such words are used, it is punishable by up to one month in jail and a fine of 50,000 baht. It is up to the court itself to decide if criticism is "honest."

In essence the new law places the Constitutional Court on the same level as the three courts in the traditional court system. Criticism of proceedings, verdicts or rulings of the Criminal, Appeal and Supreme Courts can be deemed contempt, with the judges of those courts themselves ruling on, and punishing, alleged offences.

The protection for the Constitutional and other courts also differs from criminal defamation, which is punishable by up to two years in prison, but which must be filed through the police.

The new law allows the Constitutional Court to deem verbal or written attacks a "violation of court powers," enabling it to initiate its own cases.

"What constitutes a violation is still broad and unclear," said Yingcheep Atchanont, the "housekeeper" of legal monitoring group iLaw. "Now that the law has been passed, the Constitutional Court should refrain from using this law or not use it at all."

The clause "violation of court powers" constitutes something new, said Mr Yingcheep, explaining that in the past, problematic criticism could be dealt with under the defamation law, which would put it in the hands of a different court.

"But a 'violation of court powers' is a special charge. Once the court sees the offence, they can become the defendant, investigator and judge," he said.

The Constitutional Court has been involved in some of the political tumult since 2005. One of its rulings invalidated the 2006 election, undermining then-prime minister Thaksin Shinawatra.

Another unseated prime minister Samak Sundarvej because he had received payment for a cooking show on TV.

The court has been criticised for favouring the traditional ruling class, including the army. That criticism may be ruled illegal from now on.

"Many times in the past, the Constitutional Court has ruled on cases that have had political significance, such as the nullification of elections," said Yingcheep.

"Therefore, it is a normal consideration for citizens to criticise court rulings, one way or another. There will be people who both agree and disagree. Therefore, this power over 'violation of court power,' or the limiting of criticism against court rulings, needs to be applied with an understanding of social dynamics and politics."

The new law also grants the Constitutional Court authority to settle legal disputes between state agencies, as well as allowing citizens to petition some complaints directly to the court.