Sir Jeffrey Donaldson has defended his party's intention to attempt to thwart an Assembly Bill to boost integrated education.
The Private Member's Bill, put forward by Alliance MLA Kellie Armstrong, proposes the setting of minimum targets for the number of children being educated in integrated schools, as well as providing dedicated funding for facilitation of the sector.
Currently just 7% of children in Northern Ireland attend schools in the formally integrated sector.
But Sir Jeffrey said many schools in the dominant controlled and maintained sectors welcome pupils from different and diverse backgrounds.
He contended that the Bill would see schools outside the formally integrated sector losing out on funding.
Sinn Fein MLA Pat Sheehan criticised the DUP's plan to veto the Bill as "yet another shameful stunt".
Many schools' representative bodies are also opposed to the Bill, claiming that the proposed legislation is flawed and will educationally disadvantage more than 90% of pupils.
The Bill is set to reach the final stage of the legislative process at Stormont on Wednesday.
Sir Jeffrey said the DUP will pursue a petition of concern, a voting mechanism which enables large parties to effectively block change even if a majority of other MLAs agrees to it.
The mechanism was a peace process construct designed to offer protections for minorities but it has become regarded as controversial with parties using it for issues unrelated to the traditional community divide, such as on same-sex marriage and to prevent the censure of party ministers.
It is not yet known if any of the other parties will back the DUP's petition of concern on the integrated education Bill.
Sir Jeffrey challenged Ulster Unionist Party MLAs to sign the petition of concern.
"We want a level playing field, we want to ensure that as we move forward we do so on the basis of consensus and therefore we are opposed to this Bill," he said.
"Attempts have been made to amend the Bill, they have been rejected and therefore we will be pursuing a petition of concern and I would call upon the Ulster Unionist Party in particular to add their names to that petition of concern to protect primary schools and secondary schools in constituencies right across Northern Ireland that face real problems with securing much-needed funding if this Bill goes through.
"This Bill, we are told, is about promoting integration and equality but actually this Bill undermines the principle of equality in Northern Ireland, it undermines the principle of parental choice. That is wrong and that is why we are opposing it and will be pursuing a petition of concern."
Mr Sheehan described the threat to use the petition of concern on the Bill as "shameful".
"The irony is, the DUP are using a mechanism which has not been deployed in this mandate in an effort to prevent children being educated together," he said.
"This is yet another example of the DUP's opposition to progressive change.
"The DUP is bringing its internal turmoil, dysfunction and disarray into the Assembly and into our education system. Other parties have worked collectively to help ensure that families who wish to send their children to an integrated school will have that choice.
"While the DUP, driven by electoral panic, are appealing to the most backward-looking elements of unionism, Sinn Fein in partnership with other progressive parties will continue to play our part in breaking down barriers across society and building a shared future for all."