Donald Trump's shifting statements on abortion has led a major pro-life group to back Texas Sen. Ted Cruz.

National Right to Life's political action committee said Monday it will support Cruz because he is the only candidate "who has always been pro-life." The endorsement comes after front-runner Donald Trump made several differing statements over the past week on abortion.

Trump, who in 1999 described himself as "very pro-choice," said during an MSNBC town hall last week that if abortion were illegal then women should be punished if they have an abortion.

His campaign soon walked back that statement, saying that the abortion provider should be punished and not the woman.

Trump later said in an interview excerpt from CBS' "Face the Nation" that aired on Friday that currently the laws are set and "we have to leave it that way."

The campaign sent another statement on Friday saying that the businessman gave an "accurate account of the law as it is today." Trump would change the law through his judicial appointments, the statement added.

National Right to Life said that not only is Cruz's position more consistent on abortion, but he stands a better chance in the general election against Hillary Clinton.

The endorsement comes as voters in Wisconsin go to the polls Tuesday for the presidential primary, with most polls showing Cruz ahead. The RealClearPolitics polling average has Cruz at 39 percent and Trump at 34.5 percent, with John Kasich bringing up the rear with 20 percent.