That's hydrogen sulfide (H2S), and it can ruin the wine.
First course of action is to stir the wine really well in a ventilated area. This will drive off the H2S. Hit it with a double-dose of K-meta. If you can't at early enough, this may be all you need to do.
If you get an off-taste afterward, then mercaptans formed, and you will need further treatment.
FYI -- H2S is typically caused by stressed yeast, meaning there was insufficient nutrient. In the future, add yeast nutrient to the must when starting.