The US Supreme Court on Wednesday made it easier for older workers to sue their employers for age discrimination, ruling that employers may be held liable even if they intended no harm.

The case, which applies to 70m people aged 40 and over, could have big implications for US employers. But the ruling made clear that the threshold for proving unintentional age discrimination will be set quite high, offering some protection to employers who fear being swamped by such lawsuits.