||In response to massive destruction of the landscape and significant air pollution due to brown coal mining and usage, in 1991 the Czech Government set territorial limits for brown coal mining in the North Bohemia coal basin (the ‘Territorial Environmental Limits’). In 2015, however, this 24-year-old prohibition was lifted at one of two open pit mines under the ban and, as a consequence, some of its reserves of brown coal may be mined in future. We use the regional technology-rich energy system optimization model, TIMES, to analyse the impacts of maintaining the ban versus three options for less environmentally stringent mining policies – the policy adopted in 2015 and two additional policy propositions which would further lift the ban at the second open pit mine, which have not been rejected by the Czech government. We evaluate the effects of these four policy options on the Czech energy system, the costs of generating energy, air quality and greenhouse gas emissions, and related external environmental and health costs up to 2050. We find that none of the three new policy variants jeopardizes achievement of the 2030 carbon reduction targets. However, the 2050 80% carbon reduction target may not be achievable in any case – the projected reductions range between 66 and 71%, and only maintaining the 1991 ban could reduce this gap, whereas the two policies under discussion would mean that reaching this target would be even more challenging. The newly adopted 2015 policy will lead to at least 709 PJ more brown coal use and up to 85 Mt more greenhouse gases emissions by 2050. The additional supply of brown coal made available by lifting the limits will exceed domestic demand. Brown coal that will be burnt in domestic power plants will lead to additional external costs due to adverse impacts on the environment and human health of up to €306 million.