Toyota Motor Corp. and Mazda Motor Corp. are pressing for an incentive package of at least $1 billion from U.S. states trying to land their $1.6 billion joint car factory, according to sources familiar with the negotiations.

Toyota and Mazda plan to brief their boards on a short list of states contending for the plant in the coming weeks and announce a final selection by the end of year, the sources said.

Scott Vazin, a Toyota spokesman, and Jeremy Barnes, who represents Mazda, both declined to comment.