HARARE (Reuters) - Zimbabwe put on trial on Monday an activist pastor accused of attempting to subvert the government, a charge that carries up to 20 years in prison on conviction, following protests last year against President Robert Mugabe s handling of the economy. Evan Mawarire, through his #ThisFlag movement, led a stay-at-home demonstration in 2016, the biggest protest in a decade, via a social media campaign that urged citizens to speak out against economic problems and government failure to pay workers. Mawarire was arrested again for subversion on Sunday as he stepped down from his pulpit after police accused him of circulating social media posts that accused the government of wrecking the economy. Appearing in maroon slacks at the High Court, the clergyman pleaded not guilty to two charges of subverting the government and two charges of inciting public violence. The latter carries a penalty of up to 10 years in jail. State prosecutor Chris Mtungadura said social media posts by Mawarire last year were meant to incite the population to overthrow the government. The state has lined up eight witnesses.  He was exercising his constitutional rights of challenging the policies of government. This ... was done in a lawful manner,  defense lawyer Harrison Nkomo told the court. Over the last few days, shortages of basic goods and fuel have emerged, resulting in panic buying by consumers. Shortages of cash, which started last year, have worsened, with some banks unable to provide money at all to customers. Prices of imported goods, including cooking oil and dairy products, have also risen, and businesses say they are being forced to buy foreign currency on the black market at a premium, raising fears of a return to hyperinflation. In 2009, the government adopted the U.S. dollar as its official currency, alongside the British sterling and South African rand, which helped to stabilize prices.  But the U.S. dollar has disappeared from banks and on Monday, buying $100 on the streets through a bank transfer cost $150, up from $133 a week ago, in a sign that dollar bank balances are fast losing value. The domestic quasi-currency  bond note  introduced last year to try to ease the shortages is also in short supply as it has been sucked out of the banking system but can be found on the street. Although bond notes have a 1:1 face value with the U.S. dollar, one needs $1.20 in bond notes to buy $1. Mugabe, 93, has held power since Zimbabwe won independence from Britain in 1980 and critics accuse him of using the security forces to crack down on dissent.  