Developer Forest City Ratner is considering putting up a pre-fabricated, 34-story apartment tower as part of its Atlantic Yards project in Brooklyn.

It would be the first residential building to go up at the site, which includes the Nets basketball arena already under construction.

The pre-fabricated housing would include roughly 400 apartments, and about half of them would be rented at below market rates. It's supposed to be less expensive to build this kind of housing — which would likely reduce construction costs, a sore point for some trade unions worried it would mean fewer construction jobs.

In a written statement, the Building and Construction Trades Council said it's concerned about the safety and quality of modular construction, as well as its impact on jobs and wages.

Forest City said pre-fab technology could allow for more efficient development, and eventually translate into more affordable housing and more union jobs. A spokesman for the developer said it would never build something that isn't safe. The company said while its exploring the modular option, it's pursuing conventional construction as well.