BMW said no final decision has yet been reached
Oxford's Mini plant says that an extra 50 agency staff have been told not return to work.
This takes the total figure of agency jobs cut to 430.
Last year owners BMW said 290 agency staff would go. Earlier this month they revealed the number was nearer 380 but now more cuts have been made.
BMW said: "The employees were to act as holiday cover. However, with fixed holidays now in place, the staffing is, regrettably, no longer required."
Fixed holidays were brought in for employees in 2009 and the Friday late shift has also been scrapped.
BMW added: "We appreciate that this is a difficult situation for these agency workers.
"Their contractual agreements state that any negative hours will be reclaimed. However, the company is looking in to the matter with the agencies and union, and no final decision has been reached."
BMW said it is responding to a severe drop in car sales.
Production stopped for a month-long Christmas break on 5 January before closing again for three days, only five days later.
According to the Society of Motor Manufacturers and Traders, Mini sales in the UK fell by more than 32% in December compared to the same month in 2007 and total UK car sales were down by 11% to 2,131,795 for 2008.