Jet Propulsion Laboratory scientists and engineers sued NASA and the California Institute of Technology on Thursday, challenging extensive new background checks that the space exploration center and other federal agencies began requiring in the wake of the Sept. 11 terror attacks.

The lawsuit says NASA is violating the Constitution by calling on employees — everyone from janitors to visiting professors — to permit investigators to delve into medical, financial and past employment records, and to question friends and acquaintances about everything from their finances to sex lives. Those who refuse could lose their jobs, the suit says.

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"They don't tell you what they're looking for, they don't tell you when they're looking for it, they won't tell us what they're doing with the data," said plaintiff Susan Foster, a technical writer and editor at JPL for nearly 40 years.

The lawsuit was filed in U.S. District Court in Los Angeles by 28 plaintiffs. Many have worked on such projects as the Mars rovers, the Galileo probe to Jupiter and the Cassini mission to Saturn, but none are involved in classified work, according to the suit. It seeks class-action status to represent similar JPL employees.

JPL employees have until Sept. 28 to fill out forms authorizing the background checks. Those who don't will be barred from JPL and be "voluntarily terminated" as of Oct. 27. A request for a preliminary injunction blocking the requirements is to be heard in court Sept. 24.

Caltech was sued because it manages JPL for NASA and employs its staff. The suit also named the Department of Commerce, which is involved in promulgating federal identification standards.

"It's our policy not to comment on matters in litigation," said JPL spokeswoman Veronica McGregor.

In June, JPL workers who consider the background checks unnecessary and intrusive aired their complaints before NASA Administrator Michael Griffin.

Griffin said that it was a "privilege to work within the federal system, not a right" and that he would carry out the order unless it was overturned in court, according to a video of the meeting obtained by The Associated Press.

The lawsuit was announced at a press conference at the Pasadena offices of their lawyers. A group of the plaintiffs who attended described their situation as having to choose between leaving jobs they love and giving up their constitutional rights.

Attorney Dan Stormer said the employees were being forced to "voluntarily" sign forms opening up every detail of their personal lives to federal scrutiny for two years whether or not they keep their jobs.

A 2004 Homeland Security presidential directive mandated new security badges for millions of federal workers and contractors.

The suit claims NASA and the Commerce Department went well beyond the directive, which it said was concerned "exclusively with the establishment of a common identification standard" and "contemplates no additional background investigation or suitability determination beyond that already required by law."

Foster said she will resign before the badges are required, and that there were members of the clerical staff who were too frightened about losing their jobs to come forward.

The suit claims violations of the Constitution's 4th Amendment protection against unreasonable search and seizure, 14th Amendment protection against invasion of right to privacy, the Administrative Procedure Act, the Privacy Act, and rights under the California Constitution.

Plaintiffs in the lawsuit include senior research scientist Robert Nelson, a 27-year veteran who leads NASA's New Millennium Program, which tests or validates new technology NASA will use in space; William Bruce Banerdt, project scientist for the Mars Exploration Rovers; and Julia Bell, a senior engineer who has served on the navigation team for the Mars Odyssey and rover missions, among others.

Dennis Byrnes, a flight dynamics engineer who has worked on trajectory designs for Galileo and the Apollo moon landings, said he fears the requirements will prompt people to flee government service.

The plan is a "flawed promise of security at the expense of freedom," he said.

Data collected from NASA missions and instruments by those plaintiffs who are researchers is in the public domain and shared with the scientific community, the suit said.

"Indeed, many of the plaintiffs have elected to work only on non-classified work expressly so their research can be subject to peer review, (and) they can collaborate with the best scientists worldwide and publish their results," it said.