We studied the role of fundamental constants in an updated recombination scenario, focusing on the time variation of the fine structure constant α and the electron mass m_e in the early Universe. Using CMB data including WMAP 5-yr release, and the 2dFGRS power spectrum, we put bounds on variations of these constants, when both constants are allowed to vary, and in the case that only one of them is variable. In particular, we have found that -0.019 < Δ α / α_0 < 0.017 (95% c.l.), in our joint estimation of α and cosmological parameters. Finally, we analyze how the constraints depends on the recombination scenario.