A branch of the National Institutes of Health is investigating three Veterans Affairs Medical Centers for performing experiments on patients without their consent, CNN has learned.

The probe comes in advance of a congressional hearing next week into similar charges at the West Los Angeles Veterans Affairs Medical Center, the largest veterans hospital in the country.

The three new targeted veterans facilities are in Philadelphia, Cincinnati and Tampa. Florida.

"Research is important to our veterans, but it has to be done correctly," says U.S. Rep. Terry Everett (R-Alabama). "You can't take veterans and treat them like animals by ignoring their requests that they don't want to be guinea pigs, and then doing this experimentation anyhow."

The chief research officer for the Department of Veterans Affairs tells CNN he thinks the investigations in Tampa and Cincinnati involve private medical centers that have close relationships with the veterans hospitals, and is not sure whether they involve veteran patients.

Cheryl Alvarado has been asked to testify next week at the congressional hearing in Washington. In 1995, her father, Robert Hanson, 71, died after treatment at the West Los Angeles facility.

She says he was given experimental drugs. No one from the hospital would comment, but Alvarado says she was told her father died of a heart attack.

"I think that people should go into the hospital feeling the doctors are going to help them, not go in there and have something done to them that shouldn't have been done to them," she says.

One noted expert on medical ethics says that informed consent is important because patients may not realize that the main purpose of research is producing knowledge, not helping patients.

"We have to have some protection to make it as safe as possible and that people get enrolled only when they are as aware as they can be that this is a research project," Alex Capron says.

The problem is deemed so serious that more than 1,000 research projects have been suspended at the West Los Angeles facility. Whether similar actions will take place at the three additional facilities under scrutiny remains unknown.

In all, 173 Veterans Affairs facilities treat more than 1 million U.S. veterans each year.