In answer to UUP criticism about a joke on the botched RHI scheme, Lord Morrow said "he has never encountered such conduct or abuse" in 40 years in politics.
Rosemary Barton, UUP MLA for Fermanagh South Tyrone said Lord Morrow "should catch himself on" branding his joke about the £85k a day scheme "shameful".
In a statement, that said he would not be responding to the criticism, Lord Morrow said: "It is disappointing to see the vile commentary currently circulating, particularly from other so-called unionists.
"Such actions could be expected from Sinn Fein, however it is extremely difficult to understand the motivation of those who call themselves unionists when they become engaged in this vitriol."
He went on to blast the UUP's role in securing the Good Friday Agreement, saying: "Let it never be forgotten, this was a pact formed by the Ulster Unionist Party when they were in the majority and the out workings of that saw them punished repeatedly by the electorate, not least by the releasing of terrorist criminals and the destruction of the RUC.
"When they cry humility, they need to look to their own dealings and ask how they have morphed from being unionists to supporting a nationalist/republican agenda.
"There is no doubt that agenda is an attempt to the remove the leader of unionism - Arlene Foster. This must not be allowed to happen, and I am confident the unionist community will not permit it.
"No-one in unionism should be an enemy. Opposing views are the mainstay of debate, and not opportunities to insult, decry or abuse and join with the traditional enemy.
"I have been an elected representative for in excess of forty years, which included the worst days of The Troubles yet I never experienced such venomous, spiteful, personal attacks which are presently being levied at my party and our leader," he added.
"I have always tried to maintain conduct in both the Assembly chamber and with people in general. My record speaks for itself and I am content to stand over it.
"I am unapologetically a unionist and have confidence in the electorate. I am honoured to be a member of the DUP and to serve under our leader Arlene Foster, and nothing will diminish or detract from that overall sentiment."