Baroness Mone is accused of benefitting from a company she recommended for a Covid contract.
The new Christmas Eve walkout threatens to hit celebrations and travel over the festive weekend.
Services across England and Wales affected, but life-threatening calls will be responded to.
The drugs would be used to stop more cases of the bacterial infection that has killed some children.
The alleged incident happened while the monarch was on a walkabout during a visit to Luton.