E. Gjergo & P. Kroupa have proposed a new foreground cosmic microwave background radiation (CMBR) component produced by dust associated with the progenitor clouds at z = 15─20 that led to the formation of massive early-type galaxies, calculating that a minimum of 1.4% and a maximum of 100% of the whole CMBR radiation would be produced by this mechanism. Here, I check how much dust emission is compatible with the spectrum of the CMBR monopole flux measurements within the corresponding errors. COBE-FIRAS monopole is fitted to different models with different dust emissivity spectral indexes (β) and dispersion of redshifts of the progenitor clouds (σd). Within the realistic values of β ≥ 0.5, σd ≥ 0.8, the contamination of CMBR flux by high z dust should be <1.3% (95% CL).