Two high-ranking House Democrats are calling on their Republican counterparts to end their congressional investigations of Planned Parenthood -- or at least expand them to encompass alleged misdeed by antiabortion activists who put the group's fetal tissue practices in the spotlight.

Rep. John Conyers (Mich.), top Democrat on the House Judiciary Committee, and Rep. Elijah Cummings (Md.), top Democrat on the House Oversight and Government Reform Committee, said in a letter to the Republican chairmen of those committees that the undercover videos that sparked the investigations are unreliable and may have been obtained by illegal means, calling on them to "halt these one-sided investigations immediately."

Judiciary Committee Chairman Bob Goodlatte (R-Va.)  announced Wednesday that the committee's first hearing would take place next week, titled, "Planned Parenthood Exposed: Examining the Horrific Abortion Practices at the Nation's Largest Abortion Provider." Two other committees -- Oversight, and Energy and Commerce -- are also expected to conduct hearings in the coming weeks, as congressional Republicans press an effort to strip Planned Parenthood of federal funding once the fiscal year lapses  Sept. 30.

[Parade of Planned Parenthood hearings begins next week]

Conyers and Cummings take aim at the practices of the Center for Medical Progress, the antiabortion activist group that gathered undercover video over the course of months capturing Planned Parenthood executives speaking coarsely at times about the group's practices of harvesting fetal organs and tissue for medical research. The activists allege that Planned Parenthood has broken federal laws against selling fetal tissue and against conducting "partial birth" abortions.

Planned Parenthood has strongly denied any wrongdoing, and last week, it alleged that the videos released by the Center for Medical Progress were incomplete and deceptively edited. The group has also gone to court in California to prevent the release of footage it says was illegally recorded at a conference of abortion providers there.

Conyers and Cummings contend in the letter that they have seen "no credible evidence that [Planned Parenthood] has done anything unlawful" and that the congressional investigations cannot proceed "based on the potentially illegal actions of a radical anti-abortion group that has admitted to falsifying documents, lying to their own contributors, and deceptively editing secretly-recorded videos in a three-year crusade against Planned Parenthood."

"Millions of women across the country rely on Planned Parenthood for critical health services, and they should not be denied their rights under the law and the Constitution based on the Center for Medical Progress's warped -- and ultimately unsuccessful -- effort to entrap Planned Parenthood," they write.

They continue: "However, if you choose to move forward, we request that our committees also investigation the actions of David Daleiden and his organization, the Center for Medical Progress, which -- in contrast to Planned Parenthood -- may have violated numerous state and federal laws in their clandestine effort to roll back the rights of millions of women across the country who rely on the legal and critical health care services provided by Planned Parenthood every day."

A Republican Judiciary Committee aide said in response that "it is Congress’ responsibility to investigate Planned Parenthood because this organization receives significant funding each year from the federal government."

"While Planned Parenthood and its allies would like to shift the focus onto the group that performed the undercover investigation, it does not change the barbaric findings of the Center of for Medical Progress, an organization that, to my knowledge, receives no federal funding," the aide said.

The Center for Medical Progress has dismissed Planned Parenthood's allegations that the tapes were unfairly manipulated, calling them a "desperate, 11th-hour attempt to pay their hand-picked 'experts' to distract from the crimes documented on video."