The PCS union, which represents the striking workers, has warned there will be a “significant impact” on the delivery of passports due to the strike.
Members are asking for a 10 percent pay rise, job security, changes to their pensions and protected redundancy terms.
The Government has said the demands are unaffordable and would cost £2.4billion to put in place.
PCS general secretary Mark Serwotka said: “This escalation of our action has come about because, in sharp contrast with other parts of the public sector, ministers have failed to hold any meaningful talks with us, despite two massive strikes and sustained, targeted action lasting six months.