Houston -

Police are investigating allegations that a Houston doctor is breaking the law.

Protestors and several police surrounded the Texas Ambulatory Surgical Center of Dr. Douglas Karpen on Thursday morning.

Karpen is under fire from pro-life advocates who accuse him of performing illegal, late-term abortions.

Day Garner, president of National Black Pro-Life Union said, “Our question is, why is he still open? Why is he being allowed to do horrible things to children? Why is he killing children?”

Some critics are comparing Dr. Karpen to Philadelphia abortion doctor, Hermit Gosnell, who was found guilty of three counts of first degree murder in the House of Horrors case.

In May, three women who say they are former employees of Karpen's clinic taped a video accusing the doctor of performing abortions on women after they were 24 weeks pregnant, even though it's illegal to do so in Texas.

The video was made in connection with the anti-abortion group, Operation Rescue, whistle blower program.

The program offers a cash reward for information leading to the arrest and conviction of doctors who perform illegal late-term abortions.

Local2's Mary Benton tried to enter the clinic to get the doctor or a staff member to comment, but a Houston police officer locked the door.

Dr. Karpen has not been charged with anything.

Police have not said how long the investigation will take.