Here is a very interesting article by legal scholar Christopher Slobogin about the Federal Government being involed in "transaction surveillance,"gathering large amounts of personal information from private databases, very much worth reading.

the quote has some weird spacing, sorry.....

"Many impor tant aspect s of our lives are inscr ibed in
wr it ten and digit ized records, housed in private businesses,
government agencies and other inst itut ions. These records
include a ll sor t s of information abou t us: r epor t s on our medical
status and financial condit ion; data about our purchases,
rentals, real estate holdings, licenses, and member ships; logs
list ing the dest inat ion of our emails and our Internet
wander ings; and count less other bit s of individua l descr ipt or s,
ranging from salary levels to college grades to dr iver 's license
number s. Whether the informat ion memor ializes our own
ver sion of per sonal act ivit ies or is created by the record-holder
it self, there is often an explicit or implicit under standin g that
the informa t ion will be used or viewed by a limit ed number of
people for circumscr ibed purposes. In other words, we consider
the cont ent s of many of these recor ds pr iva t e, vis-a -vis most of
the wor ld.
Thus, it may be surpr ising that law enforcement officials
can, per fect ly lega lly, ga in access to all of this informa t ion
much more ea sily than they can sea rch our houses or even our
ca r s. While the la t t er types of a ct ions requir e probable cause,
government can obtain many of the records just descr ibed
simply by asking (or pa yin g) for them.1 And, at most , all the
government needs to show in order get any of these r ecords is
tha t they ar e “ r elevant ” t o a government invest iga t ion–a much
lower , and much more diffu se, level of just ifica t ion than
probable cause.2
This state of affairs might make sense when the records
sought ar e t ruly public in natur e. It might also be just ifiable
when the recor ds involve an ent ity such as a corpora t ion,
professional service provider , or government depar tment and
are sought in an effor t to invest igate the ent ity and its
member s. But today, facilit a t ed by the comput er iza t ion of
information and communica t ion, government routinely obt a ins
personal medical, financia l and ema il records, in connect ion
with invest iga t ions tha t have nothing to do with business or
governmen ta l

...

In cont rast , t ransact ion su rveillance, whether it is event -
ba sed or target -based, never requir es probable cause or
reasonable suspicion, even when conducted by government
agents whose pr imary goal is cr iminal invest igat ion. At most ,
government agent s seeking t ransact ional informat ion need a
subpoena–either a subpoena duces tecum issued by a grand
jury, or an “ administ rat ive subpoena” issued by a government
agency–which is valid as long as the in format ion it seeks is
“ r eleva n t ” t o a legi t ima t e (s t a t u t or ily-a u t h or ized )
invest igat ion. Relevance, as defined by the Supreme Cour t , is
an ext remely low standard. In the grand jury context , a
subpoena may be quashed on ir r elevancy grounds only when
the cour t “ det ermines that ther e is no reasonable possibility
that the category of mat er ials the Government seeks will
produce informat ion r elevant to the general subject of t h e grand
jury's invest iga t ion.” 35 The r elevancy st a n da r d in the
administ rat ive subpoena context is even lower ,..."