I am certain the unions will cooperate with reducing costs, as they have done before. But they want the normal way of negotiations between company and employees, not a set reduction in pay because a politician thinks it helps him get votes next elections.
The big mistake the unions make is that they view the Dutch government as a government willing to spend money on KLM. Actually, the Dutch government has no intention of spending money on KLM and thus the Dutch government (but we see the same in France) set conditions which ensure KLM will pay back its loans. This view isn't that odd as the Dutch government is very reluctant to provide free money towards specific companies. Thus, for the Dutch government these guarantees and loans are just business.
BTW it will help them at the next elections as any specific deal for KLM would discriminate against other companies. This deal give them an argument against those who arguement against those against any state aid and those who think the government should help. Moreover, it ensures that the Dutch government can show consistency internationally.
I am not saying conditions aren't logical, but the way the government decided pilots should be the ones to pay for the loans is a departure of the normal ways reorganisations and state aid have been organised.
The government has already given billions to other companies, including air traffic control, the railroada, bus companies, etc, without those strict conditions and terms they applied to KLM and without always wanting that money back.
So the "discrimination" is allready in place.
But while that can possibly be explained, the specific rules regarding the reduction in salaries is a very significant departure from how things were organised before corona.
When the banks required and were gifted many more billions KLM has " the privilege" the loan, there were no requirements regarding pay of bankers, or management.
There might have been demands for reducing expenses, but no detailed demands on how to achieve that. It was always a thing a company resolved with the unions/workers.
If it really was only business, they would require KLM to be able to pay back the loans. The best way would be to make sure expenses are less than income so there is money left to return to the banks.
Demanding the 15% cutback in costs is therefore reasonable, but why did they not stop there and demanded a specific pay cut of the pilots? That is more than business, that is pandering to the envious people who might thereafter vote for you.