Ad referendum

adverb, adjective
subject to agreement by others and finalization of details: an ad referendum contract
Historical Examples

But as I see no authority for it other than mere tradition, I believe my share of it, and take it ad referendum.
From London to Land’s End Daniel Defoe

In other words, I have only voted “ad referendum,” and I ask that my statement be entered in the protocol.
International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884. Various

Those of Amsterdam remain here, because they have no need of an ad referendum.
The Diplomatic Correspondence of the American Revolution, Vol. IX Various