The phrase "onerous conditions" means having difficult, burdensome, or unpleasant requirements or circumstances that are demanding and make a task or situation challenging. Full definition
As mentioned above, contracting States of the Convention should not impose more onerous conditions on the recognition or enforcement of international arbitral awards than those imposed on domestic arbitral awards. (terralex.org)
But it's also meant the most onerous condition on Unlimited Choice has been removed. (tomsguide.com)
Not only are the repayments extensive but the PFI buildings remain owned by the original company and can therefore come with onerous conditions regarding their upkeep, including non-negotiable costs for routine maintenance jobs, such as repainting or changing bulbs. (schoolsweek.co.uk)