About 6.5 million Americans paid an average penalty of $470 for not having health insurance in 2015—20 percent fewer than the year before, according to data released Tuesday by the IRS.

The IRS collected $3 billion, IRS Commissioner John Koskinen said in a letter to members of Congress.

The individual mandate is the most unpopular part of Obamacare, surveys show, and both Republican congressional leaders and the incoming Trump administration have pledged to repeal it.

If they don’t, the 2017 penalty for adults will be the same as in 2016 — $695 or 2.5 percent of household income, whichever is higher. In 2015, the penalty was $325 or 2.5 percent of income.

About 85 percent of 2015 tax returns processed so far indicated taxpayers had qualifying health coverage all year, up from 81 percent for 2014, which the IRS reported last January.

Almost 13 million taxpayers claimed one or more health care coverage exemptions.

About three-quarters of the taxpayers who reported owing the tax payment also said they were due a refund, the IRS said.

The agency cautioned that some data from 2015 is still being reviewed and its findings disclosed Tuesday were preliminary.

This article was originally published by the Kaiser Health Network.