'a voluntary action' is correct and usable in written English.
You can use this phrase to refer to an action that someone does voluntarily or willingly; often without being asked or prompted. For example, "The animal rescue shelter was grateful for his voluntary action of fostering a stray cat."
However, this would be a voluntary action on the officers' part.
Apparently, the manner in which the photo-enforcement law was written made compliance a voluntary action.
He argued that the ultimate reality lying behind appearance is what he referred to as 'will', which manifests itself in us whenever we perform a voluntary action.
At the 21st session of the United Nations Framework Convention on Climate Change (UNFCCC, COP21), a voluntary action plan, the '4 per 1000 Initiative: Soils for Food Security and Climate' was proposed under the Agenda for Action.
The State Council, China's cabinet, said Thursday that fixing the target for 2020 was a "voluntary action" taken by the Chinese government "based on our own national conditions," according to the state-run news agency Xinhua.
In a repeated-measures design, 26 females participated in a double-blind, placebo-controlled trial to test the effects of 0.5 mg testosterone on SoA, using an implicit measure based upon perceived shifts in time between a voluntary action and its outcome.
While believing isn't a strictly voluntary action, when it comes to disputed questions like this we can decide which way to jump.
Hours before the HHS secretary's speech before the National Academy of Medicine, the major pharmaceutical lobbying group announced a new voluntary action that would, instead, direct consumers to company websites with pricing information.
Hours before the HHS secretary's speech, the pharmaceutical industry's major lobbying group announced a new voluntary action that would instead point viewers of TV commercials to company websites with pricing information.
The degree of beta suppression has been associated with the likelihood that a new voluntary action will need to be actuated (Jenkinson & Brown, 2011; Wyart etal., 2012).
In such a case the voluntary action which is of the essence of the right of expatriation is lacking.
