The Belfast Telegraph understands many on the list have not paid dues and in some cases missed several deadlines to do so.
Letters are to be sent informing individuals they cannot take part in the vote on Wednesday, September 22, despite an amnesty offer by party chairman David Campbell a few months ago.
Mr McCrea said: “I can confirm I did formally ask to see the membership list when I submitted my nomination papers last week.
“I think it is only fair that I get the list so I can see who the people are I have to canvass. But so far it has not been made available.
“This is the first time that we have held a one member, one vote election for party leader and it is imperative that those who are entitled to vote are able to.”
And, in the background, the selection of the party’s candidates for next year’s NI Assembly election is also causing waves.
The sitting MLA, and Deputy Assembly Speaker, David McClarty faces deselection after the UUP’s East Londonderry election committee failed to select him as a candidate. Only the party’s Executive Committee can save him. But he’s already quoted as as being “devasted” by the decision.
Today a BBC report adds
Another Ulster Unionist MLA may face deselection following a vote in Upper Bann on Wednesday night.
George Savage came fifth in the selection meeting. His Assembly colleague Sammy Gardiner came third.
The poll was topped by Colin McCusker, son of former MP Harold, while Craigavon councillor Joanne Dobson came second.
On Monday, Ulster Unionists in East Londonderry chose two other candidates ahead of deputy speaker David McClarty.
The party’s Westminster candidate Harry Hamilton came fourth.
It is understood the party is planning to run three candidates in the constituency.
They tried three candidates in East Londonderry in 2007.
Update The BBC report is misleading, unless Harry Hamilton has switched constituencies since this year’s general election – which is unlikely to say the least.
More likely is that he came 4th in Upper Bann selection poll.
And that three candidates will be selected there.
We’ll have to wait to see what the final candidate lists, in both constituencies, look like.