He added that the court's doubt "hardens into conviction when we consider the consequences" of permitting such suits to be brought.
That permitted civil suits against racketeers who gutted companies.
Included, for example, has been a law permitting suits against countries that the government labels sponsors of terrorism.
California, Georgia and Missouri have passed laws permitting suits against the managed-care companies.
A two-year-old Texas law permitting such suits is being tested in the courts.
But in a number of recent cases, federal courts made exceptions that permitted suits in state courts.
The Jencos' suit was filed under a 1996 federal law permitting suits against countries that sponsor terrorism.
The bill's backers defeated two efforts to permit certain suits to proceed even if the immunity legislation passes.
The Bivens doctrine has been extended to permit suits against private employees who are performing government functions.
The vote was 5 to 4 in two other sections of the opinion, permitting suits based on negligent manufacture and failure to warn.