Up to 30,000 people may not have the proper photographic ID to allow them to vote in Northern Ireland's assembly election.
Electoral Office said 6,000 people applied in the past three weeks
However, the Electoral Commission, the government appointed body which monitors elections, has said it made every effort to encourage people to apply for special cards.
It is the first election anywhere in the UK where people will require photographic ID to vote in an effort to combat electoral fraud.
A driving licence, EU passport or Translink Smartpass will do. A further 90,000 people have applied for special photographic ID cards since they were introduced.
However, Seamus Magee - head of the Electoral Commission - said there was still a problem.
"There are approximately 30,000 people, who if they turned up to vote, would not have the applicable ID," he said.
"Obviously for some operational reasons some people have not received cards," he said.
"We understand that from the Electoral Office this morning that in the region of 1,500 people who have applied either applied late, or there are other reasons why the card has not been delivered.
"This would be because they weren't on the register or that the information on the application form did not match up with the information provided on the registration form."
The Electoral Office said 6,000 people applied in the past three weeks. About 2,000 ID cards were posted out on Saturday and a further 1,000 on Monday.
However, June Butler, the assistant Chief Electoral Officer, said some people who did apply would be disappointed.
"Some 800 of the applications have not been possible to be processed because they are inaccurate. There are identifiers on the application forms that don't match with the data that we hold, therefore there are about 800 rejections," she said.
Meanwhile, candidates for the assembly election have begun their final day of campaigning ahead of Wednesday's poll.
About 20 different parties and groupings will contest the election.
In all, 256 candidates are nominated for the poll that will elect 108 MLAs (Members of the Legislative Assembly).
The assembly was suspended more than a year ago and the parties are going into the election against the background of a deadlocked political process.
A power-sharing executive will not be re-established at Stormont immediately after the election.
Instead, a review of the workings of the Good Friday Agreement and a further round of negotiations is expected to begin.
Observers from the Electoral Commission will be operating at polling stations in all constituencies across Northern Ireland for the first time during the election.
Nearly half of all polling stations will be visited at some time
during the 15 hours of voting - 270 polling stations out of 612.
There are 18 observers, one for each constituency, and each will visit 15
Meanwhile, Prime Minister Tony Blair has said the future of Northern Ireland is now in the hands of the electorate.
On Monday, Mr Blair said: "This election will be a very big moment for people in Northern Ireland.
"We are now at the point in the politics of Northern Ireland where I can't make any more decisions - I can't renegotiate agreements, I can't rewrite those things that have already been agreed.
"The decision is now for people in Northern Ireland and they are going to have to decide, in a fundamental way, whether Northern Ireland today is a better place than it was six, seven, 10 years ago."