PIERRE, S.D. (KELO) — Donations from anti-tax groups are fueling the drive to pass Amendment C in South Dakota’s June 7 primary elections, but the opponents have brought in nearly twice as much.

The campaign finance report filed Monday by South Dakotans Against Higher Taxes that supports the measure shows no direct contributions from anyone but also lists $566,564.75 of donated goods and services from Americans For Prosperity and two other groups. Another $50,000 donation came after the pre-primary reporting deadline.

Representative Jon Hansen of Dell Rapids and Senator Lee Schoenbeck of Watertown convinced enough fellow Republican legislators last year to steer the measure onto the June ballot so it could be in effect before the November statewide vote on expanding Medicaid eligibility. Senators voted 18-17 for the June date, followed by the House 51-17.

Amendment C’s supporters spent $339,423.39 last year.

The main opposition group, South Dakotans for Fair Elections, reported it still had $624,371.48 cash on hand, after raising $1,505,960 and spending $881,588.52.

The largest contributions by opponents included $455,960 from the National Education Association, $250,000 from Avera Health, $250,000 from Sanford Health, $250,000 from Washington, D.C.-based The Fairness Project, $150,000 from Monument Health and $150,000 from the American Cancer Society Cancer Action Network.

Amendment C would change the South Dakota Constitution to require 60% support for approval of ballot measures raising taxes or fees or obligating more than $10 million in any of the first five years.

Many Republican legislators have long opposed expanding Medicaid eligibility. At least one expansion measure called Amendment D will be on South Dakota’s general election ballot in November. Many of the groups that oppose Amendment C support Amendment D.