Etherington's comments follow the recent Charity Commission decision to allow two-fifths of trustees at the CfBT Education Trust to receive remuneration.
It has since emerged that a number of other charities already plan to follow suit (Third Sector, 25 October).
"The NCVO upholds the voluntary principle," Etherington will tell a gathering of trustees. "Voluntary trusteeship remains a key principle of charity. It is essential that this is not lost."
While trustees cannot be paid for their duties, the new Charities Act allows them to be paid for other services without asking the commission for authorisation.
Etherington will also set out the NCVO's agenda in a speech at its AGM in London today. He will say that the organisation's future focus must lie in a "continual process of transformation".
"By that I refer to a much broader context than just public service delivery," he will tell members.
One of the NCVO's immediate priorities will be a transformation of relationships between local government, individuals and the community through the Local Government Bill.