The scientists say more artificial light could mess with sleep patterns, animal migrations, plant growth, and even food security.
Night skies are already 10% brighter because of existing satellites. Ruskin Hartley from DarkSky International called out the "dangerous glare or blinding flashes" these new mirrors could create.
Professor Charalambos Kyriacou added that darkness is vital for plants and food production.
So far, neither company has responded to these concerns.