Projects were run on an entirely voluntary basis by the people involved.

The consent is entirely voluntary and may be changed or withdrawn at any time.

Note that taking any form of positive action is entirely voluntary.

For the appeal, the project was made entirely voluntary and opened to the entire school.

To critics, Chinese officials note that the program is entirely voluntary.

The work is now again carried out on an entirely voluntary basis.

Your share of the debt is an entirely voluntary burden.

As part of the "Big society", surely they should be run on an entirely voluntary basis?

Based on the assessment they may be offered the program which is entirely voluntary.

They believed that it should be entirely voluntary, and a right, not a punishment.