  Most of relatively warm, unevolved metal-poor stars ($T_{\rm eff}\gtrsim
5800\,\mathrm{K}$ and $[{\rm Fe/H}]\lesssim -1.5$) exhibit almost constant
lithium abundances, irrespective of metallicity or effective temperature, and
thus form the so-called Spite plateau. This was originally interpreted as
arising from lithium created by the Big Bang nucleosynthesis. Recent
observations, however, have revealed that ultra metal-poor stars (UMP stars;
$[\mathrm{Fe/H}]<-4.0$) have significantly lower lithium abundances than that
of the plateau. Since most of the UMP stars are CEMP-no stars, carbon-enhanced
metal-poor stars with no excess of neutron-capture elements, a connection
between the carbon enhancement and lithium depletion is suspected. A
straightforward approach to this question is to investigate carbon-normal UMP
stars. However only one object is known in this class. As an alternative, we
have determined lithium abundances for two CEMP-no main-sequence turn-off stars
with metallicities $[{\rm Fe/H}]\sim -3.0$, where there are numerous
carbon-normal stars with available lithium abundances that can be considered.
Our 1D LTE analysis indicates that the two CEMP-no stars have lithium
abundances that are consistent with values near the plateau, which suggests
that carbon enhancement and lithium depletion are not directly related.
Instead, our results suggest that extremely low iron abundance is a fundamental
cause to depleted lithium in UMP stars.
