The plant, located in Palmela just south of Lisbon, is to close on 17, 18, 21, 22, 23 and 24 March in order to better "regulate" production, the company said.
Autoeuropa had previously ordered down days in December 2015 and January 2016 totalling 27 days.
The plant currently assembles the Volkswagen Scirocco, Sharan and the Seat Alhambra, with a new model only set to be produced in Portugal mid-2017.