Foreign companies seeking to acquire sensitive US assets could face fines running into the tens of millions of dollars if they violate agreements with a secretive US government panel that vets deals on national security grounds.

The inter-agency panel, the committee on foreign investment in the US, or Cfius, is applying pressure on some companies to agree to new potential financial penalties. One attorney familiar with the situation says the government in one case opened negotiations by proposing penalties worth 10 per cent of a company’s sales.

The threat of fines provides further evidence of the growing obstacles facing non-US companies as they seek to gain regulatory approval for takeovers in sensitive sectors such as telecommunications and defence.

Some attorneys who handle Cfius cases question whether the panel has the legal authority to demand financial penalties beyond the myriad export-control regulations that already carry financial penalties.

The Bush administration has stepped up its scrutiny of foreign takeovers since the backlash last year against Dubai Ports World’s takeover of five US port terminals.

Clay Lowery, the Treasury department’s assistant secretary for international affairs, said the government had included provisions calling for “civil action” in mitigation agreements before the Dubai controversy, but acknowledged that Cfius was agreeing to more mitigation agreements than it has in the past.

“There are concerns probably that we are being too tough – we don’t dismiss those concerns. There are those that follow what we do and think we aren’t being tough enough. We are trying to get the balance right,” Mr Lowery says.

Such conditions range from ensuring that employees are properly screened before handling sensitive materials to creating separate subsidiaries to manage work for the US government.

The strategy of imposing financial penalties marks a relatively recent development.

Paul Marquardt, a partner at Cleary Gottlieb who handles Cfius cases, said he was aware of recent instances in which the government had made “astronomical” requests for penalties worth hundreds of millions of dollars in the event of a violation of a mitigation agreement.

Ultimately, the companies – which Mr Marquardt would not identify – agreed to penalties that were “very high” but below the government’s initial demand.

“I think that it is understandable that they are trying to figure out how these agreements should be enforced, but they tend to ask for things that are well out of proportion of penalties of violating other laws,” Mr Marquardt says.