  The high-redshift radio-loud quasar PKS 2126-158 is found to have a large
number of red galaxies in close apparent proximity. We use the Gemini
Multi-Object Spectrograph (GMOS) on Gemini South to obtain optical spectra for
a large fraction of these sources. We show that there is a group of galaxies at
$z\sim0.66$, coincident with a metal-line absorption system seen in the
quasar's optical spectrum. The multiplexing capabilities of GMOS also allow us
to measure redshifts of many foreground galaxies in the field surrounding the
quasar.
  The galaxy group has five confirmed members, and a further four fainter
galaxies are possibly associated. All confirmed members exhibit early-type
galaxy spectra, a rare situation for a Mg II absorbing system. We discuss the
relationship of this group to the absorbing gas, and the possibility of
gravitational lensing of the quasar due to the intervening galaxies.
