Border Force members of the Public and Commercial Services union (PCS) are in dispute with the Home Office and are striking over pay, pensions, jobs and redundancy.
The first walkout over 23-26 December passed off without significant disruption, though, with Heathrow claiming travellers experienced "no issues", and there being few additional reports of major delays or hiccups.
Walkouts were also staged at Birmingham, Cardiff, Gatwick, Glasgow and Manchester airports, and had threatened to disrupt up to 10,000 flights between 23 December and 31 December.
The PCS union has warned the action could continue until May following a successful strike ballot in November.
