Thirty members of a Malaysian opposition party have been charged with plotting to overthrow the government after they were arrested on the way to an event promoting a mass political rally next month.

Police say the 30 Socialist Party of Malaysia members, including a member of parliament, were arrested Saturday because police found leaflets and t-shirts promoting an outlawed communist party on their bus. The 16 men and 14 women have been remanded in custody for a week.

Opposition leaders denounced the arrests as a clumsy attempt by police to discourage attendance at the July 9 rally, which has been called by a loose alliance of lawyers and interest groups to press for electoral reform.

Socialist Party leader Nasir Hashim was quoted Monday in the Malay Mail newspaper saying the charges are “absolute nonsense.”

The 30 are charged under a seldom-used law that makes it a crime to try to wage war against Malaysia's constitutional monarch. The charges carry the possibility of life imprisonment.

Hashim said the only t-shirts provided by the party carried the group's list of demands for clean elections. He said some members of the group may have had other t-shirts purchased in public markets in Kuala Lumpur.

The rally, organized by a group calling itself “Bersih,” or “Clean,” hopes to bring tens of thousands of people to the capital to demonstrate for electoral reforms ahead of balloting expected within the next year. Government officials say the rally is illegal.

Bersih last organized a mass rally in 2007, attracting an estimated 30,000 people before police broke up the protest with tear gas and water cannons. The opposition coalition led by Anwar Ibrahim made major gains in elections the next year, ending the ruling party's two-thirds majority in parliament.