Universities and companies are joining forces to lobby Congress to keep a tax provision that allows employers to give staff as much as $5,250 in yearly tax-free tuition help.

The tax-overhaul package passed by the Senate earlier this month includes the provision, which has been part of U.S. tax law since the late 1970s. The House version would require employees to pay taxes on the benefit for the first time. Congressional leaders are working to send a final bill to President Donald Trump by Christmas.

Hewlett...