Hawaii families struggling with school costs could get help from a new federal tax-credit program, but Governor Green faces a tough political call on whether to join it.

• A new federal program starting next year would help families cover school costs, at both public and private schools.
• Hawaii's teachers union opposes it, saying it uses taxpayer money to fund private school tuition.
• The union backed Green in his last two elections, so opting in risks angering a key supporter.
• The plan may also clash with Hawaii's constitution, which bars public money from going to private schools.
• Under the program, people who donate to scholarship groups get up to $1,700 back in tax credits, and local scholarship demand already outstrips supply.

Outlook: Analysts expect Hawaii to opt in eventually, but Green is likely to hold off in the near term over the legal and political risks.