Texas Gov. Rick Perry on Wednesday signed an anti-abortion-rights group's presidential pledge, making him the seventh Republican presidential candidate to do so.

Perry's decision strengthens his hand with conservative voters while drawing attention to front-runner Mitt Romney's decision not to sign on. Candidates Herman Cain, Jon Huntsman and Gary Johnson have also so far refused to sign the pledge and are under pressure to do so.

"I not only pledge to protect unborn life, but have a record of doing so in Texas," Perry said in a statement. "I have signed legislation requiring parental consent for a minor to obtain an abortion, and have long advocated adoption as an alternative to abortion in order to protect unborn children."

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The Pro-Life Presidential Leadership Pledge was developed by the Susan B. Anthony List. It binds candidates to four principles:

• Nominating conservatives to the federal bench;

• Selecting "only pro-life appointees" to relevant executive-branch positions, in particular the head of the National Institutes of Health, the Department of Justice and the Department of Health and Human Services;

• Fighting for legislation that would permanently end all taxpayer funding of abortion, both domestically and internationally, and defund Planned Parenthood and all other contractors and recipients of federal funds whose affiliates perform or fund abortions; and

• Advancing federal legislation — the Pain-Capable Unborn Child Protection Act — that would ban abortions after 20 weeks from fertilization.

"Gov. Perry has been a longtime friend of, and leader for, the pro-life community," SBA List President Marjorie Dannenfelser said in a statement. "His signature on our pledge is more than welcome, and we applaud him for his commitment to continue to fight for women and unborn children."

Candidates Michele Bachmann Michele Marie BachmannEvangelicals shouldn't be defending Trump in tiff over editorial Mellman: The 'lane theory' is the wrong lane to be in White House backs Stephen Miller amid white nationalist allegations MORE, Thaddeus McCotter, Ron Paul, Rick Santorum and Newt Gingrich have already signed the pledge since it was first announced in June. Tim Pawlenty had also signed the pledge before dropping out of the race earlier this month.