nadobowiązkowy in inglese:

That organization depends on voluntary contributions.

Participation is voluntary and free of charge.

It must be your voluntary decision.

voluntary obligations

She did a lot of voluntary work for the Red Cross.

He made a voluntary contribution to the school.

The company appealed for people to take voluntary resignation.

Participation in the competition was voluntary.

It was his voluntary decision to leave a well-paid job and go to India.

Your presence here is voluntary.

Have you ever had any sex that was voluntary?

As was the case the first time, the new program will be voluntary.

Micheal put in for the answer in voluntary way.

When I was at university I took three months out to travel around Latin America and I got involved in some voluntary work in Costa Rica.

That company aims to reduce employee numbers by arranging a lot of retirement money for voluntary redundancies.