  We determine the pressure dependence of the electron-phonon coupling constant
in $\kappa$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$ by comparison of high pressure Raman
scattering and high pressure infrared reflectivity (IR) measurements. We use
comparison of the IR reflection spectrum from deuterated and protonated samples
to aid the deconvolution of several overlapping phonon modes. These coupled
modes are modelled with a Green's function to extract the linear pressure
dependence of the individual modes. The Raman active molecular vibrations of
the BEDT-TTF dimers stiffen by 0.1-1 %GPa$^{-1}$. In contrast, the
corresponding modes in the IR spectrum are observed at lower frequency, with a
pressure dependence of 0.5-5.5 %GPa$^{-1}$, due to the influence of the
electron-phonon interaction. The stronger pressure dependence of the central
C=C mode of the BEDT-TTF molecule in the IR, is discussed. Our analysis
suggests that reduction of electron-phonon coupling under pressure does not
account for observed suppression of superconductivity under pressure.
