The pharmaceutical industry is expected to try this month to lobby its way out of giving seniors enlarged discounts on Medicare drugs, putting insurers, hospitals, and patient groups in a defensive posture.

The pharmaceutical industry has one last chance in 2018 to get Congress to undo the added discounts it must provide to seniors in Medicare’s drug coverage gap, which requires seniors to pay high out-of-pocket costs for drugs. Congress must pass legislation by Dec. 7 to fund the government, and — opponents suspect — the pharmaceutical industry will try to attach language to the spending bill to change the discounts and reap a $4 billion windfall.