There's only a few days left to get major discounts on a Tesla Model 3 and 4 other EVs

The two cheapest versions of the Tesla Model 3 will become ineligible for any tax credits on January 1. George Rose/Getty Images

• The federal EV tax credit rules are getting a major overhaul on January 1.
• Discounts of $7,500 or $3,750 will soon be taken at purchase instead of later.

The rules for lucrative tax credits that can effectively lower the price of an electric vehicle by up to $7,500 will get stricter on January 1, meaning fewer vehicles will be eligible.

Popular vehicles like Tesla's Model 3 — one of the best-selling EVs in the US — and Ford's Mustang Mach-E, for example, will no longer qualify as new rules about where components are sourced kick in. Now, those with components made in China or from a Chinese-owned company no longer qualify, the Treasury Department said.

Some manufacturers, like Tesla, have already warned their models will no longer be eligible. Others have said they're hopeful theirs still will, as the complex rules that confuse buyers also keep automakers scratching their heads.

Of course, income rules and other pricing limits still apply, but the tax credit will soon be applied at the time of purchase to lower its price instead of retroactively at tax time.

Here's the list of models that may no longer qualify after January 1, leaving just a few days to get a discount: