Sir Jeffrey Donaldson has denied that there was a 'side deal' between the DUP and the Tories over disclosure of political donations.
The DUP MP was reacting to a tweet posted by Seamus Magee, the former Head of the Electoral Commission.
In it he said that the failure to publish past political donations "must be" part of the DUP's deal with the Conservatives
Secretary of State James Brokenshire announced yesterday that only donations from July 1 this year will be published, even though he had the power to backdate them to 2014.
The Tories had pledged to provide greater transparency around political donations in their election manifesto.
Unlike in Britain, the identities of donors to parties in the north have remained secret due to concerns about their security.
But critics have suggested the ban is harming accountability.
Mr Magee, a retired head of the Electoral Commission in Northern Ireland, tweeted: "The deal on party donations and loans must be part of the DUP/Conservative deal. No other explanation."
Sir Jeffrey told the BBC it was "absolutely not" true that there was any side deal on donations.
"Let me be absolutely clear. I was deeply disappointed to read Seamus Magee's tweet last night. Totally innacurate.
"And I hope that Seamus, a man of integrity whom I respect, will take my word for it.
"There is no side deal on party political donations."
The DUP has confirmed it received a Brexit donation worth around £435,000 from a group of pro-union business people.
The money from the Constitutional Research Council was spent on pro-Brexit advertising throughout the UK.
Ann Watt, head of the Electoral Commission, said the first donation and loan report is due to be published in the autumn.
But she said the commission would like to publish past donations.
"While all reportable donations and loans received from July 1 2017 will now be published by the Commission, we would also like to see the necessary legislation put in place, as soon as possible, to allow us to publish details of donations and loans received since January 2014," she said.
Sinn Féin's leader in Northern Ireland, Michelle O'Neill, criticised Mr Brokenshire.
She said he had "quite crassly let the DUP off the hook on the issue of the Dark Money donation of over £400,000 which bought its support for Brexit".
"This latest evidence of a Tory side deal with the DUP comes on the heels of the DUP’s support for cuts to the wages of emergency and public sector workers and support for a Tory Brexit," she said.
Alliance MLA David Ford accused Mr Brokenshire of failing to properly address the issues.
"There are many questions as to why donations during the Brexit campaign, during the election campaigns of this year and the election campaign of last year are not fully transparent and open," he said.
"At a time when there is such deep cynicism in this society about the political process, his failure to address that issue properly can only enhance that suspicion and that cynicism.
"We need to see openness, we need to see full transparency and we need to see Parliament backdating that to January 1 2014."
Green Party leader Steven Agnew said Mr Brokenshire's announcement on donations was "long overdue but falls short as past details will remain hidden".
