"The injunction against the charter amendment bill reinforces the red shirts' view that the judicial odds are stacked against them," said Thitinan Pongsudhirak, a political analyst at Bangkok's Chulalongkorn University.

"Their street mobilization this time sends signals they will not stand by and be disenfranchised yet again," he added.

The red shirts chose June 24 for their latest gathering as it marks the anniversary of a revolution that brought an end to absolute monarchy in 1932.

Thaksin has been accused of republican leanings - taboo in a country where the king is revered by many - although he has always denied that.

To the anger of some red shirts, Yingluck has ignored calls to amend lese-majeste laws that can give lengthy prison sentences to those found guilty of insulting the royal family.

(Editing by Alan Raybould and Ed Lane)