What's the law regarding labeling a varietal wine and possible additives of cheaper grape juices into it?

Some varieties taste suspiciously like concord grape juice. I'm sure there must be a law regarding the content and percentage permitted for a wine to allow secondary grape juices or cheaper additives to be mixed into the final wine.

But, on the label, I see no list of ingredients such as on beer. So, it could be 51% of what the label states and 49% of something cheaper, possibly, maybe?

In the United States the label will state what type of wine is in the bottle. If it is labeled as a specific type of wine, such as Cabernet Sauvignon, this means that at least 75% of the wine was produced from Cabernet grapes. Blending juice from other types of grapes is a common practice and often will improve the flavor and aroma of the wine.

According to law, the contents have to agree with the label.

Are you going to file a suit? Seeking what damages?