The phrase "a voluntary commitment" is correct and usable in written English.
It can be used to describe a promise or obligation that someone willingly takes on without coercion.
Example: "The organization encourages a voluntary commitment to community service among its members."
Alternatives: "an optional pledge" or "a willing obligation".
More than 6,000 European cities have signed up to the Covenant of Mayors, a voluntary commitment to go faster and further than EU climate targets.
It's a voluntary commitment, and it's much smaller than most environmentalists believe is necessary to avoid a big spike in carbon emissions.
Co-operatives, as internationally recognised by (among others) the UN, are member-owned and controlled ventures, with membership entirely a voluntary commitment.
By the completion of both meetings, over two dozen businesses had signed a voluntary commitment to support these three principles of social responsibility.
Affirmative action is largely a voluntary commitment by leading institutions that are convinced it is in their self-interest to enlarge opportunities for historically disfavored groups, because it helps fulfill their missions.
Trump could decide as early as this week whether the United States will remain in the historic Paris agreement, which reflects a voluntary commitment by the world's governments to reduce their carbon emissions.
"This is a historic voluntary commitment," said Eron Shosteck, a spokesman for the Alliance of Automobile Manufacturers, an industry lobbying group that oversaw the joint safety effort.
If they make a public, voluntary commitment, they'll try to follow through.
Just recently, there was news of a "historic voluntary commitment" by the auto industry to make S.U.V.s safer.
The proposed relocation, which would start as a one-year pilot programme, would focus only on Syrians who have been recognised as refugees in Italy and Greece and would depend on an initial voluntary commitment from member states.
California state Sen. Mark Leno (D), who has introduced legislation that would require every phone sold in that state to have a kill switch, called the voluntary commitment "an incremental yet inadequate step to address the epidemic of smartphone theft".
