BARCELONA, Dec 13 (Reuters) - Volkswagen (VOWG_p.DE)"s Spanish unit SEAT has added new output curbs at its main assembly car plant near Barcelona in December, closing its factory for five days, because of global semiconductor supply bottlenecks, the company said on Monday. SEAT has decided to advance by one week its production break before the Christmas holidays, which was originally planned to start after Dec. 23 but it will now be after Dec. 16. "The crisis of global semiconductors supply, that affects all the automobile industry, will force us to idle the Martorell plant on 17, 20, 21, 22 and 23 December," the company said on Monday in a statement. The production curbs come as demand for the SEAT and CUPRA brands is back at pre-pandemic levels, the statement said. The company will also close down the next week on Jan. 3, 4 and 7, as Jan. 5 and 6, are holidays, it added. SEAT has curbed its production several times all along 2021, including a partial idling of the plant, in late August. The Martorell plant assembled around 500,000 cars in 2019, before the start of the pandemic. Carmakers around the world have been forced to make sharp production cuts this year as supply chain disruptions and booming demand for consumer electronics have led to an acute shortage of microchips that takes more time to ease than expected. Chips have become a critical component in automobiles, powering devices ranging from fuel injection to entertainment systems.