The Literal Commandment
On this same day you shall make a proclamation as well; you are to have a holy convocation. You shall do no laborious work. It is to be a perpetual statute in all your dwelling places throughout your generations. (Leviticus 23:21)
The literal commandment is that we should do no laborious work on the fiftieth day after Passover: the Feast of Weeks (Shavuot).