Education Reform Now — the advocacy organization now chaired by former Chancellor Joel Klein — unveiled a TV spot today that shows relatively senior teachers arguing against seniority.

The ad’s debut corresponds with Mayor Michael Bloomberg’s escalating campaign against the “last-in, first-out” law that requires the city to lay off teachers according to their seniority. It shows three city teachers with between four and 21 years of experience in the New York City schools saying that if the city has to lay off teachers, it should do so based on merit. The ad doesn’t say how the city should define merit, or what constitutes a great teacher, questions that the city will have to confront if the law does change. It also doesn’t name the city’s teachers union, like its previous more aggressive ads.

A spokesman for the group, Stefan Friedman, said the ad cost ERN “seven figures,” and would run for a month in Albany and New York City. He would not give the exact cost.

The ad features Jane Viau, a former investment banker-turned-teacher at Frederick Douglass Academy I who has already spoken out against the seniority law as a board member of Educators 4 Excellence, another advocacy organization that opposes the law.

“It is illogical and I feel it is irresponsible,” Viau says of the law in ERN’s ad.

Thus far, United Federation of Teachers President Michael Mulgrew’s argument against changing the law is that there’s no need to debate it because the city doesn’t need to lay off teachers this year.