Most Free Presbyterians are deeply troubled by the prospect of Ian Paisley in government with Martin McGuinness, a close friend of the DUP leader says.
Ian Paisley is head of the Free Presbyterian Church
The claim was made by the Reverend Ivan Foster, who is a senior minister in the Free Presbyterian church.
Mr Paisley is the moderator of the church.
Rev Foster was speaking just 36 hours before the DUP and Sinn Fein are due to nominate their choices for first and deputy first minister.
"The thought of one so highly esteemed and loved as Ian Paisley in political coalition with Martin McGuinness I would say is heartbreaking to most, if not every, Free Presbyterian," Rev Foster said.
He was being interviewed for BBC Newsline, which can be seen at 1830 GMT on Thursday.
Reverend Ivan Foster said Free Presbyterians are troubled
Mr Paisley said it was a church matter and he would not be making any comment.
On Wednesday, Northern Ireland Secretary Peter Hain warned the DUP there would be consequences if it did not indicate its nominee for first minister on Friday.
"It is not a question of jumping first," Mr Hain told the House of Commons.
"If there is not a willingness to express even an intention to nominate on Friday for March 26, what is the point of proceeding?"