All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Forcing people to close their shops at prayer times is something which is praiseworthy in religion. That is because establishing the prayers (at their prescribed fixed times) is one of the most important pillars of Islam after the two declarations of faith. So ordering people to perform the prayer and notify them to perform it in congregation in the mosque is enjoining people to do good. If people were not obliged to close their shops, many of them would fail to attend the prayer in congregation and remain busy in selling and buying and neglect the mention of Allaah. This is something that Allaah does not like and is not pleased with. Allaah says (which means): {Men whom neither trade nor sale (business) diverts them from the remembrance of Allaah, nor from performing the prayers.}[24:37]. Moreover, the Prophet said: "Whoever hears the call to the prayer, and does not come to it, his prayer is not valid except if he has a sound excuse." [Al Haakim, Ibn Maajah, and Ibn Hibbaan] Therefore, it is an obligation on whoever hears the call to perform the prayer with the congregation in the mosque, and whoever fails to do so, then the Muslim leader can force him to do so. It is reported in a narration: "No, by Whose Hand my soul is, [you will not do your duty] until you force them to abide by the truth (i.e. Islamic legislations)." [At-Tirmithi and Abu Daawood]
Allaah knows best.