As the British Parliament debates allowing Chinese telecom giant Huawei to build major portions of its 5G infrastructure, Congress is joining the Trump administration to try to persuade the government of Boris Johnson to just say no — or suffer real consequences.

On Friday, three GOP senators wrote to the members of the British National Security Council to urge them to bar Huawei from playing a role in their next-generation telecom networks.

“This letter represents a genuine plea from one ally to another. We do not want to feed post-Brexit anxieties by threatening a potential U.S.-U.K. free trade agreement when it comes to Congress for approval. Nor would we want to have to review U.S.-U.K. intelligence sharing,” wrote Sens. Marco Rubio (R-Fla.), Tom Cotton (R-Ark.) and John Cornyn (R-Tex.). “The facts on Huawei are clear. We hope that your government will make the right decision and reject Huawei’s inclusion in its 5G infrastructure.”

The letter comes on the heels of a new bill introduced by Rep. Jim Banks (R-Ind.) last week that would outright halt U.S. intelligence-sharing with countries that use Huawei tech in their 5G infrastructure. These congressional efforts are meant to bolster the Trump administration’s extensive efforts to convince British leaders that Huawei technology represents a security vulnerability that could impact the U.S.-British relationship.

President Trump reportedly called Johnson late last week to urge him not to allow Huawei in Britain’s 5G plans. A senior U.S. delegation traveled to London two weeks ago, led by deputy national security adviser Matthew Pottinger, to hand over materials meant to convince British officials the risks of using Huawei equipment for 5G cannot be effectively mitigated from a national security point of view.

At the Raisina Dialogue in New Delhi earlier this month, Pottinger said, “Can you imagine [Ronald] Reagan and [Margaret] Thatcher having a conversation in the 1980s saying, ‘Let’s have the KGB build our telecommunications systems, because they’re giving us a great discount.’ ”

Secretary of State Mike Pompeo tweeted Sunday in support of British Member of Parliament Tom Tugendhat’s argument that keeping Huawei out of Britain’s 5G plan was an issue of sovereignty. The data flowing over Huawei’s networks, Tugendhat has said, can be appropriated by the Chinese government, which by law can request any data managed by any Chinese company anywhere.

British intelligence and cybersecurity agencies have gone back and forth on whether they believe the risks of building 5G based on Huawei equipment can be properly mitigated. Johnson hinted Monday that he would seek a compromise plan that would allow Huawei into British 5G systems with some as-yet-unspecified restrictions that are meant to placate Washington.

The U.S. senators argue that given the way 5G is structured, with a heavy dependence on software integration, there’s no way to have some parts of it built on Huawei tech while protecting other parts at the same time. The fact that Huawei would be in control of ongoing software updates means that the risks would only increase over time. “The economic arguments in favor of Huawei fall apart when the costs of risk mitigation are included,” they wrote.

Even as they urge Britain to reject Huawei, the senators tacitly acknowledge that alternative options are scarce and potentially expensive. Congress is considering legislation to create a fund to support 5G research, they wrote, adding that if Britain goes with Huawei now, the market space for alternatives will only shrink over the long run. Meanwhile, Huawei has benefited from more than 20 years of huge Chinese government subsidies, allowing the company to drastically underbid its international competitors and warp the market even further.

“We believe it is in the best interests of the United Kingdom, the U.S.-U.K special relationship, and the health of a well-functioning market for 5G technologies to exclude Huawei,” the senators wrote. “No one can compete with a company that has the Chinese government absorbing its losses.”

The British decision on Huawei should take into account the overall Chinese government strategy to use its national champion companies to expand its international reach, said Klon Kitchen, senior fellow for technology at the Heritage Foundation.

“For U.K. security in general, they will have adopted a critical vulnerability, not just from a cybersecurity standpoint but from a political influence standpoint,” he said. “They will have worked hard to reassert sovereignty in the wake of Brexit only to run into the arms of the Chinese Communist Party.”

The British decision could also set the precedent for several other European countries considering whether to allow Huawei tech into their 5G plans. European countries may save money now by allowing Huawei into their networks. But if the Trump administration and Congress are right, they will pay a far higher cost when they realize later they have made a huge mistake.

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