Arkansas Gov. Mike Beebe has vetoed what would have been the most restrictive abortion ban in the nation.

The measure would have banned most abortions once a fetal heartbeat can be detected using an ultrasound, which is usually 12 weeks into a pregnancy. The governor told lawmakers the bill is unconstitutional.

Beebe used the same reasoning last Wednesday when he vetoed a 20-week abortion ban. Lawmakers quickly overrode that veto in a 53-28 vote.

The Democratic governor said the Arkansas legislature's new Republican majority is violating the Supreme Court's Roe v. Wade decision.

Seven states have enacted 20-week abortion restrictions. It's based on the argument that an unborn baby can feel pain as early as 20 weeks into a pregnancy.