Owners of electric cars in Vermont recently got a letter from the Department of Motor Vehicles with some bad news. Starting Jan. 1 they would have to pay $178 a year to register their cars, twice as much as owners of vehicles with internal combustion engines.

In imposing the higher fee, Vermont became the latest state to make people pay a premium for driving electric. At least 39 states charge such annual fees, including $50 in Hawaii and $200 in Texas, according to the National Conference of State Legislatures.

Now, as President Donald Trump rolls back Biden administration measures to promote electric vehicles, Republicans in Congress are considering imposing a national fee to bolster the fund used to finance roads and bridges, a fund that is in dire shape.

The fees are an attempt to make up for declining revenue from gasoline taxes that electric cars, for obvious reasons, don’t pay.

Environmentalists and consumer groups agree that electric vehicle owners should help pay for road maintenance and construction. But they worry that Republicans, who control Congress, would set the fee at extremely high levels to punish electric vehicle owners, who tend to be liberals.

That has already happened in Texas and other states, said Chris Harto, a senior policy analyst at Consumer Reports who focuses on transportation and energy.

“EV owners should contribute to paying for the roads that they use,” he said. But, he added, “in some cases, states are implementing fees that are pretty punitive to EV drivers, significantly more than what the owner of a gas vehicle would pay.”

Flat fees are also unfair to low-income drivers or people who don’t drive very much, making it even harder for them to buy cars that pollute less, Harto and others said. Federal and state gasoline and diesel taxes are levied per gallon, so that people who drive more — or own gas guzzlers — automatically pay more.

The main reason that revenue from fuel taxes has declined is that internal combustion engines have become much more efficient, while political leaders have been reluctant to raise fuel taxes to keep up with inflation.

The federal gas tax of 18.4 cents a gallon has not been increased since 1993. The Highway Trust Fund, which finances transportation projects from proceeds of that tax, could become insolvent by 2027 without new sources of funding, analysts say.

There are 5.4 million electric vehicles on U.S. roads, according to the Alliance for Automotive Innovation, an industry group. But that is roughly 2% of the total and not the main cause of revenue gaps.

“Lawmakers are finding a convenient scapegoat, and penalizing the cleanest vehicles on the road while ignoring the real cause of the shortfall,” said Max Baumhefner, director for EV infrastructure at the Natural Resources Defense Council.

Some of the highest electric vehicle fees are in states that elect Republicans, like Texas, Wyoming and Ohio, all of which charge $200 a year on top of the regular registration fee. But electric vehicle fees are not just a red-state phenomenon. New Jersey, where the gasoline tax is more than twice as high as Texas’ relatively low 20 cents a gallon, began charging electric vehicle owners a $250 fee last year.