The DUP currently has 25 MLAs who hold the party whip, while Jim Wells, independent Alex Easton and TUV leader Jim Allister are also in favour of the petition.
That means at least two UUP MLAs would need to sign it.
Ms Armstrong’s bill would increase the number of integrated school places and set targets for the number of children being educated in such schools.
About 7% of pupils in Northern Ireland are educated currently in just under 70 formally integrated schools, which aim to mix pupils from Protestant, Catholic and other backgrounds.
However, some non-integrated schools also have a mix of pupils from different religious backgrounds as well as those who are not religious.
The head of Northern Ireland’s oldest integrated school, Lagan College, has said Ms Armstrong’s bill would “provide genuine and much-needed choice” for parents.
However, some other schools have written to parents claiming it would “elevate integrated schools” above other types of school.
Those concerns have been echoed in an open letter by five bodies that represent many schools and the four main churches.
On Monday, DUP leader Sir Jeffrey Donaldson insisted his party would try to use the petition of concern to stop the bill from passing.
I help to manage Slugger by taking care of the site as well as running our live events. My background is in business, marketing and IT. My politics tend towards middle-of-the-road pragmatism, I am not a member of any political party. Oddly for a member of the Slugger team, I am not that interested in daily politics, preferring to write about big ideas in society. When not stuck in front of a screen, I am a parkrun Run Director.