Peugeot has been criticised for not allowing a proposed 4.2% pay rise to improve redundancy payments for those about to lose jobs near Coventry.
The Ryton plant produces the Peugeot 206 model
The Ryton plant is to close in January with up to 2,300 jobs going.
The Transport and General Workers' Union (T&G) said the rise, which would come into effect on 1 January, should have an impact on redundancy payments.
Peugeot said it is offering between one and three years' salary to departing staff plus £5m of support.
The 4.2% increase will be put to workers, after unions and management agreed the figure on Thursday.
The T&G estimates about 1,200 workers at Ryton have left already, approximately 1,000 are due to follow soon and about 1,000 warehouse and office staff will remain.
It said it was disappointed "but not surprised" that the redundancy payments would be based on this year's pay.
The union said staff were going on 14 December and being put on gardening leave, but the official finishing date is 8 January.
Des Quinn, from the T&G, said: "They could have made a gesture, but it shows the contempt they've shown for the workers.
"They've broken commitments to the workforce on a number of occasions and treated them badly."
In a statement, PSA Peugeot Citroen said: "It is worth noting that we remain unable to fill over 70 redeployment opportunities within the group, illustrating employees' desire to take advantage of the strong financial package on offer.
"(The company has) put forward a strong pay deal which reflects its ongoing commitment to its employees and which the trade unions are recommending for acceptance.
"On October the 10th the group gave its employees at Ryton 3 months notice of the closure of the plant.
"This was not related to any legal requirement, but honoured the commitment to notice that the group had previously made."
The T&G added it was very pleased for remaining workers with what both sides are calling an "industry-leading" pay deal.
It had been expected that the plant would close in the middle of next year, but it was announced in October that it will shut in January.
In April, Jean Martin Folz, chief executive of Peugeot Citroen, said a study showed Ryton had high production and logistical costs leading the company to decide to move production to Slovakia.