DENVER -- It looks like Colorado voters will again be asked to decide the controversial issue of when life begins and what defines a person.

Abortion opponents have formally started the work of putting a measure on the Colorado ballot in 2010 that would give rights to human embryos.

Colorado defeated a similar measure last year by a 3-to-1 ratio.

Personhood USA, based in the Denver suburb of Arvada, said Thursday it has filed language for the proposed state constitutional amendment with the Legislative Council.

It's the first step toward getting approval for a petition to put the measure on the ballot. The group would need about 74,000 signatures.

Supporters say they're not using the word "fertilization" this time. They say that may have confused voters who may have visualized chicken eggs.

They say the new version will use the term "the beginning of the biological development" instead.

Keith Mason of Personhood USA said the 2008 election results are not a deterrent to their campaign.

"The basic reason why we are doing this again is because we are right," he said.

Planned Parenthood told 7NEWS the voters spoke last year on the issue and made it clear how they feel.