DUP MLA Jonathan Bell, tells a press conference an email was being 'withheld' from him.
He was speaking at Stormont ahead of the first minister facing a vote of no confidence over her involvement in the flawed heating scheme.
He identified the specific email as having been sent in January 2016 by the economy department permanent secretary Andrew McCormick to the head of the Civil Service with a “high” importance rating.
Mr Bell stated the exact time it was sent and also listed the recipients.
“The critical information is in that email and it should be release for public consumption,” he added.