Conservative groups came out in opposition to an increase in the federal gas tax, saying it's not needed, after President Trump said he could support a 25-cent hike as part of a deal with Congress to pay for his proposed $200 billion infrastructure plan.

"Supporters of raising the gas tax claim that roads and bridges are a priority and higher taxes are needed to pay for them. But by refusing to consider displacing existing spending, they are admitting that they view every other spending program — foreign aid, farm subsidies — as more important than fixing roads and bridges," said Grover Norquist, president of Americans for Tax Reform.

Americans for Prosperity, a group fund by the billionaire Koch brothers, highlighted comments Tuesday from Transportation Secretary Elaine Chao calling the gas tax a "regressive" levy that falls disproportionately on low-income families. "Increasing the gas tax would effectively undermine the benefits of tax reform by clawing back hundreds of billions of dollars from low- and middle-class families. We strongly urge the president and Congress to abandon the idea of increasing the federal gas tax and instead focus on spending smarter, preventing new burdens on taxpayers and breaking through regulatory gridlock," the group said.

FreedomWorks President Adam Brandon said an increase would undermine the GOP's tax cut legislation in December. "I'd hate to see a new tax siphon off 20 percent of the $1,000 tax reform bonuses back to the swamp this year."

Trump endorsed the idea at a Wednesday meeting with lawmakers, a day after Chao told reporters "the president has not declared anything out of bounds. Everything is on the table."

The federal gas tax is currently 18.4 cents per gallon for gasoline and 24.4 cents per gallon for diesel, and the funds go into the federal Highway Trust Fund. The tax has not been raised in 25 years.