In an effort to fit more packages in delivery trucks and planes, retail and e-commerce giant Amazon has reduced the amount of shipments it packs in cardboard boxes and has opted for lighter-weight plastic mailers. That move, according to waste management experts, is having a negative effect on machinery at materials recovery facilities.

According to The Washington Post, the recent holiday season was the busiest for e-commerce and created “a massive hangover of packaging waste.” Amazon is by far the biggest shipper and producer of that waste—and a trendsetter, according to the report, meaning that its switch to plastic mailers could signal a shift across the industry.

The Washington Post has more details:

Over the past year, Amazon has reduced the portion of shipments it packs in its cardboard boxes in favor of lightweight plastic mailers, which enable the retailing giant to squeeze more packages in delivery trucks and planes.

But environmental activists and waste experts say the new plastic sacks, which aren’t recyclable in curbside recycling bins, are having a negative effect.

“That Amazon packaging suffers from the same problems as plastic bags, which are not sortable in our recycling system and get caught in the machinery,” said Lisa Sepanski, project manager for King County Solid Waste Division, which oversees recycling in King County, Wash., where Amazon is based. “It takes labor to cut them out. They have to stop the machinery.”

Related:Amazon to Pay $1.5M for ‘Misleading’ Plastic Labels

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