President Donald Trump fleshed out his proposal last week to spend $1 trillion on infrastructure by listing tolling on interstate highways as one way to raise funds, but his idea is encountering reluctance in Congress.

Several key lawmakers said they were receptive to the idea, but cited obstacles to moving forward.

“Everything’s on the table: Gas tax, tolling,” said Rep. Sam Graves, chairman of the House Transportation and Infrastructure Subcommittee on Highways and Transit. “I’m not a big fan of tolling — I don’t like paying for a road twice, but that’s my opinion.”

The Missouri Republican told reporters Thursday that lawmakers were considering even politically tricky sources of money, including raising fuel taxes.

The administration raised the tolling option in a fact sheet released Tuesday, the same day as the fiscal 2018 budget request. The fact sheet lists several infrastructure proposals that were part of the budget request, but the tolling idea was listed separately.