David Cameron and Sir Reg Empey at the UUP conference last December
The Ulster Unionist leader has said the party's only MP, Lady Sylvia Hermon, is under no immediate pressure to make a decision on a pact with the Tories.
On Thursday, the parties confirmed plans to fight elections in NI on a joint ticket and under a new name.
Lady Hermon is thought to be unhappy with the arrangement but has so far made no comment.
Ballot papers will carry the title 'Ulster Conservatives and Unionists - New Force'.
Conservative NI spokesman Owen Paterson said he hoped Lady Hermon would eventually give her support.
"She's highly respected in North Down," he said.
"David Cameron has made it very clear that we do want more intelligent, well-educated, skilful, professional women politicians and Sylvia scores a lot of points on all those fronts.
"So we hope she thinks it over, and we hope she comes with us."
UUP leader Sir Reg Empey refused to be drawn on the absence at the launch of Lady Hermon saying she "can speak for herself", but said he was "delighted" by the move.
"This is something entirely new in NI, something which would allow us to become more fully and demonstrably an equal partner within the UK family."
Sir Reg added: "The UUP believes that the union is a two-way process and we believe that a pan-UK unionist vehicle is the best way of promoting the values of the union."
The pact will operate during the next European and general elections, but the two parties will remain independent of each other and have stressed it is not a merger.
The Tory-Ulster Unionist partnership has been under discussion since last July, and Conservative leader David Cameron received a standing ovation at the UUP conference in December.