The warnings come ahead of new statements about the plans by CEO Oliver Blume at the large VW factory in Wolfsburg later on Tuesday.
Previously, Blume and other representatives of the automaker have said that the cutback plans could affect 100,000 employees, after the union agreed to proposals to reduce staff by tens of thousands.
Union leader Christiane Benner has called the plans to cut costs and raise margins "madness" and local union representatives have warned of strikes if Blume does not back down.
According to critics, VW employees are now paying for years of strategic mistakes involving software and electric cars, as well as failures in the Chinese market.
