Chadian lawmakers vote on Monday on a controversial change to the constitution that will bolster President Idriss Deby's powers and which opposition groups warn will damage democracy in the landlocked African state. The text, which received the green light from the government earlier this month, must be approved by three-fifths of lawmakers in Chad's National Assembly. There was tight security in place around parliament with all the roads leading to the legislature ringed by police.Thirty-three opposition members in the 170-seat house are boycotting the vote.Two activists from the Chadian Convention for the Defence of Human Rights (CTDDH) were arrested on Monday, Mahamat Nour Ibedou, the head of the civil society group, told AFP."They wanted to stage a sit-in in front of parliament," he said. "I'm just returning from the police station where I was told they will be released in the course of the day." Tchindebbe Patalle, a spokesperson for the National Union for Development and Renewal (UNDR) opposition party said all opposition groups had "wanted to demonstrate outside parliament to protest against the vote but the security forces are posted all around."Street protests are rare in Chad, which has had a long history of coups, and has been ruled with an iron fist by Deby, 65, who is serving his fifth term, which runs until 2021. Deby has insisted the changes are necessary. The changes will increase presidential terms to six years with a limit of two terms. The current mandate is five years with no limits on re-election.The vote comes amid growing political tensions in Chad, ranked by Transparency International as one of the world's most corrupt nations, as opposition groups boycotted a forum last month discussing the proposed changes. A Western ally in combating jihadism in the volatile Sahel region, cash-strapped and poverty-stricken Chad has endured two years of severe recession worsened by a slump in oil prices. The changes do not include provisions for the creation of a post of vice president, contrary to what was proposed at a national forum on the reforms in March.The Catholic Church has warned that a new constitution "seriously risks distorting the rules of the democratic game." Opposition groups have called for the text to be put to a referendum. Deby, who has been named in a corruption probe in the United States, has said that elections on hold since 2015 will take place this year.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.