 -- The top Democrat on the House Intelligence Committee says the secret GOP memo sent to the White House -- that sources told ABC News could be released as early as Thursday -- is not the same one the committee voted to make public.

Rep. Adam Schiff tweeted Wednesday night that he had sent a letter to the Republican committee chairman, Devin Nunes, claiming that Republicans had "secretly altered" the memo after it was voted on Monday evening. Schiff charged "material changes" had been made which the committee was never apprised of.

Republicans have said the memo details FBI wrongdoing in the Russia investigation.

Schiff called the alleged changes "deeply troubling" and said "the White House has been reviewing a document since Monday night that the Committee never approved for release."

While he did not detail the changes he says were made, he called them "substantive," said there was "no longer a valid basis for the White House to review the altered document" and called on the committee's Republican majority to immediately withdraw it.

The White House did not have an immediate comment Wednesday night.