Two senators who wield considerable influence over U.S. foreign aid threatened Tuesday to withhold funding for Afghanistan if the government in Kabul doesn’t cease attempting to collect customs fines for U.S. military cargo being shipped out of the country as part of the troop drawdown.

Sen. Patrick J. Leahy (D-Vt.), chairman of a subcommittee that oversees foreign aid programs, called the Afghan government’s request that the U.S. military pay $70 million in customs fines ludicrous “after all we’ve given them.”

“I’ve seen some stupid things from that government,” he said during a hearing convened to unveil next year’s budget for the State Department and foreign operations. “I’ve seen some things that make you wonder what universe they live in — but this went beyond the pale.”

His tone, which was echoed by the subcommittee’s ranking Republican, Sen. Lindsey O. Graham (S.C.), gave voice in unusually public and stark terms to the exasperation many U.S. officials have come to feel over the conduct of Afghan President Hamid Karzai’s government.

The senators proposed in an amendment included in the draft bill to withhold $5 in aid for every $1 imposed in fines for shipping out U.S. military equipment. The bill may be amended before it comes up for a vote by the full Senate.

“It’s a subtle message which I think they will understand,” Leahy said, referring to the potential cut in Afghan funds. Graham, calling Kabul’s position “ridiculous,” said the amendment should “send a message to the Karzai government.”

In an unprecedented move, Karzai’s cabinet recently shut down Afghanistan’s land borders to U.S. shippers for about a week. Afghan officials said they took the drastic measure to compel the United States to pay fines for failing to present properly processed customs forms for the thousands of containers that are exiting the country, mostly through the Pakistani border.

The customs fight has forced U.S. commanders in Afghanistan to rely more heavily on cargo planes to ship out supplies, an alternative that costs much more than ground shipping.

U.S. officials see the Afghan request as a veiled shakedown and have declined to pay. They have sought to resolve this and similar past disputes quietly.

The latest dispute caught lawmakers’ attention after The Washington Post reported last week that the dispute over customs fines had the potential to dramatically inflate the cost of the U.S. drawdown from Afghanistan. Depending on how heavily commanders end up relying on air transport, the withdrawal is expected to cost between $5 billion and $7 billion.