LINCOLN, Neb. (AP) — Opponents of a ballot measure to expand Medicaid in Nebraska have launched a new radio ad urging voters to reject it.

The 30-second spot unveiled on Friday argues that the proposal would cost too much and allow more patients into an already crowded Medicaid system. The ad was sponsored by Americans for Prosperity-Nebraska, a Libertarian-leaning advocacy group funded by the billionaire Koch brothers.

Jessica Shelburn, the group’s state director, says allowing more people into Medicaid could stress the system that was designed for society’s most vulnerable populations.

Supporters of the measure say it would provide coverage to low-income people working jobs in construction, restaurants and other low-wage industries. The measure would extend coverage to an estimated 90,000 uninsured people.