What objections might labor raise to cooperating with management?

The main objection that labor is likely to raise to this
is that management is the enemy because management does not have the best interests of
the labor union or its members at heart.

In many cases,
labor unions feel that the employers do not want what is best for workers.  They feel
the employers will always seek to benefit the company even if that hurts workers. 
Because they feel this way, unions might feel that they are likely to hurt themselves if
they engage in any cooperation with management.  They will feel that the management's
desire to cooperate is a trick to con the union into agreeing to something that will
hurt it.