The phrase "onerous taxes" means high or burdensome taxes that are difficult or demanding to pay. It implies that the taxes are excessive or causing a heavy financial strain. Full definition
South Korea, for example, has already threatened a more onerous tax on sprits which have a higher alcoholic content than 30 % volume. (politics.co.uk)
Placing new onerous tax burdens on individual industries or sectors, many of which are already under great financial stress in this economy, is the wrong response. (bcnys.org)
A more onerous tax rate on property fund managers could dampen deal flow for that sector of the market. (nreionline.com)