Sounds like you've got mycoderma floating on the surface, a few questions before trying to diagnose it:
Does the wine have any off odors?
When is the last time that you tested for PH, TA, and SO2, without these numbers, it will be a guesstimate on how to correct it.
This is caused by a few different scenarios, one being too much head space in the carboy, another possible reason is that your sulfite level is probably real low, not adequate to protect your wine.
The good news, this is easily fixed, in most cases, unless it has been sitting like that for a while and it has a strong "rotten egg" smell, worse if it has off flavors.
I've seen this on a few batches that I had aging, I hadn't topped off enough (now I top off about 1 inch from the bung), and I hadn't tested my wine in a while.
When I tested them I found that my SO2 levels were just about depleted; I removed the film by slowly filling the carboy with distilled water (we're talking about less than a half cup) until the film was at the very top of the carboy neck about to spill over, I removed it, removed enough wine to be able to accommodate the meta that I needed to add to bring the levels back up, and actually slightly elevated to kill off any residual bacteria, I put a clean sanitized bung and airlock back in and the wine was fine.
If the wine has an off odor, the same procedure will be necessary, but you may need to splash rack, or if it persists, an addition of Redulees might be necessary.
The info that is needed to diagnose properly is:
Test results (PH, TA, and SO2) and if there is any off odors or flavors.
I hope that this helps.