Allen, (4 Wales caps) links up with the squad after Newport Gwent Dragons centre Tyler Morgan was released due to a hamstring injury.
Uncapped scrum-half Williams is called in as injury cover following Rhys Webb’s injury against Australia on Saturday.
Medical update on injuries will be made following further assessment.
Wales squad update
Wales have called Cardiff Blues duo Cory Allen and Tomos Williams into their 2016 Under Armour Series squad.
