This is usually known as 'long service leave' in English. I think the use of the word 'seniority' could potentially be confusing as entitlement to this form of leave has nothing to do with seniority (in the sense of rank) within the company, but only with long service.

-> "Long Service Leave Act 1976
Be it enacted by His Excellency the Governor of Tasmania ... Entitlement to long service leave - 7A. Subject to this Act, an employee is entitled to long service leave on ordinary pay in respect of continuous employment with an employer."
http://www.thelaw.tas.gov.au/summarize/s/1/?ACTTITLE="LONG S...

-> "The university schemes for long service leave are set out below. Staff who have had a break or breaks in service for domestic reasons (i.e. maternity leave or family commitments such as the care of relatives) ... should have any period of continuous service in employment with [..] the University of Oxford at the time of commencing each break in service for domestic reasons counted for the purposes of calculating long service leave entitlement."
http://www.admin.ox.ac.uk/ps/managers/hours/longserv.shtml

-> "3) Long Service Leave

a) Long service leave entitlement is due to staff who have completed continuous service during a leave year as follows:-
5 year’s continuous service - 1 additional day’s leave
7 year’s continuous service - 2 additional day’s leave..."
http://www.hr.soton.ac.uk/TandC/clerical/core_terms.asp