Shevuot (Oaths) 46 - Wage Dispute
If a craftsman says to his employer, "You stipulated to me a fee of two sela coins for this job," and the employer says, "I stipulated to you a fee of only one sela," - Shmuel said, "In that case the employer swears that he stipulated only one sela, and the craftsman looses the contested sela."
But why should this be so? Didn't we require the worker to swear about his wage in a similar case ? The answer is that in this other case, the employer may have forgotten which worker he already paid. However, in the case of wage dispute, the employer certainly remembers the amount of stipulation.
Art: Jean-Francois Millet - Forest workers in the wood saws