How do you report someone who lied about income to get on ObamaCare?
If a person reports income inaccurately on their Marketplace application in order to qualify for ObamaCare cost assistance that they don't deserve, their dishonesty will catch up to them when they file their tax return for the following year. If they received more cost assistance than they were due, the excess will be owed back to the government when they file their taxes.
Meanwhile, reporting other information inaccurately generally has the same effect.
If you suspect someone of reporting income or information related to cost assistance to the IRS inaccurately, this is tax fraud. You should follow the directions on how to handle such a situation.
Keep in mind that the Affordable Care Act is a flexible program. Someone may report low income, because they expect to lose a source of income during the year, this is valid. Also realize that the ACA provides subsidies on claimed income. If a person is making money they aren't claiming, this is a whole other ball of wax. Likewise, enrollment can be confusing, and people may make honest mistakes.
Anyone who mistakingly misreported incorrect information or an inaccurate income to the marketplace, or to the IRS, should make a good faith attempt to get right and correct their information ASAP.
Generally, if someone simply reports income inaccurately, but tried to report honestly, the worst that will happen is that they will lose tax credits and owe back respective amounts up to the repayment limit of their income. You can't go to jail for making a mistake or not paying the fee... you can however get in serious trouble for purposeful tax fraud.