Neighbors burning plastic

My neighbors, who are renting the house next door, have been burning plastic instead of giving it to the government-appointed ladies who come to collect it. This morning, we saw them burning it and asked them politely to stop, which they did at the time. But then they resumed burning it after sunset. They recently had a quarrel with the local leader over this issue and were warned about it. Instead of stopping, they just moved the burning to a different corner of their land, not easily noticeable from outside close to my place. I’d prefer not to engage with them directly about this, so I’m wondering if there’s a more discreet way to address the issue without confrontation.