Electroweak (EW) physics at the future electron-proton colliders LHeC and
FCC-eh is studied.
Simulated neutral-current and charged-current deep-inelastic
scattering cross sections are employed for simultaneous determinations
of the parton distribution functions of the proton together with
the fundamental parameters of the EW theory, including their
statistical and systematic uncertainties.
Uncertainties of the $W$ and $Z$ boson masses are determined and
compared to uncertainties obtained from HERA combined data.
The LHeC data will allow for a determination of $m_{\rm W}$ with an uncertainty
of 17 MeV, and the FCC-eh with 10 MeV, thus exceeding the
precision of the currently most precise single measurements.
The LHeC or FCC-eh data will allow for a precision determination of the vector
and axial-vector couplings of the light quarks to the $Z$-boson,
with uncertainties being smaller by an order order of magnitude than current measurements.
It is shown, that the measurements of the EW parameters are not
limited by the precision of the parton distribution functions, which
have also to be determined from the same data.
The measurements of the inclusive DIS cross sections as a function of
the four-momentum transfer squared $Q^2$
will allow for high precision tests of the scale dependence of the EW theory
in the range from a few GeV up to the TeV regime from a single process.