The ethics of US law firms forcing partners to retire are set to come under intense scrutiny after Sidley Austin last week agreed to fork out $27.5m (£13.1m) to settle the largest ever age discrimination case against a law firm.

US labour specialists say the settlement, which follows both the New York State Bar Association and the American Bar Association (ABA) recently denouncing mandatory retirement ages, will make it harder for US firms to remove older partners.