וביום השביעי יהיה לכם קודש (ויקהל לה:ב)

And the seventh day should be for you holy

When R’ Yehoshua Klugar zt’’l served as Rav in the city of Greiding, the townspeople’s primary source of income was selling non-kosher fish from the river flowing in the length of the city’s borders. R’ Yehoshua implored by the townsfolk to stop handling non-kosher food, though halachically, you can only sell non-kosher fish if caught randomly.  But to no avail, the Yidden continued selling the fish, which led some to transgress the Shabbos by catching and selling fish on Shabbos. 

R’ Yehoshua needed help handling the situation, So he traveled to Belz to Maran Rebbe Yehoshua zy”a to lament the problem and seek advice.  Maran Rebbe Yehoshua told him to gather all the Yidden together and warn them in his name to keep the Shabbos, and if they desecrate the Shabbos, a punishment will befall them.

The townsfolk, however, didn’t accept the Belzer Rebbe’s zy”a harsh words, and after a short time, all the fish in the river disappeared, and they lost their livelihoods.