* Supreme Court struck down tariffs, no refund guidance

provided

* New 10% tariffs imposed by Trump face legal challenges

* Fedex ( FDX ), Costco sued by customers to pass along refunds

(Adds details from court filing in paragraphs two, three and

eight and background throughout)

By Tom Hals

March 12 (Reuters) - The U.S. government's work to build

a four-part system to refund $166 billion in illegal tariff

collections with interest is between 40% and 80% complete,

according to a court filing on Thursday.

Brandon Lord, an official with U.S. Customs and Border

Protection, said in a court filing the agency is developing an

online claim portal for importers and brokers to submit refund

requests.

Once submitted, the claims will go through processing,

review and refunding, according to the filing. Lord said in a

filing last week the system could be operating as soon as

mid-April.

Lord's filing at the U.S. Court of International Trade was made

to comply with an order issued last week by Judge Richard Eaton

as part of his directive to refund tariff payments.

Most U.S. tariffs were struck down by the Supreme Court in

February, dealing a blow to President Donald Trump's central

economic policy. However, the Supreme Court did not provide

guidance on refunding the tariff payments that had been

collected from importers since February 2024.

Many large importers such as FedEx ( FDX ) sued CBP to

protect their right to a refund, which Trump said could take up

to five years. Many smaller importers feared the cost of the

refund process would outweigh the benefits of trying to get

reimbursed.

Eaton last week ordered CBP to begin processing refunds

using its existing system, but the agency instead proposed a new

process that would be ready to accept refund applications as

soon as next month and would not require importers to sue.

Lord said in Thursday's filing the least developed part of

the system was the mass processing portion, which was 40%

complete, while the most developed portion was the review

portion, which was 80% complete.

CBP did not say how quickly refunds would be paid. More than

330,000 importers paid the tariffs on 53 million shipments and

only around 21,000 were registered with its system to receive a

refund, according to a court filing last week.

Refunds will only be issued to importers who paid them.

Consumer groups and lawmakers have urged companies to pass along

the refunds to consumers, although there is no obligation to do

so.

FedEx ( FDX ) and Costco have been sued by customers for

refunds and FedEx ( FDX ) has said it will reimburse customers, while

Costco said it will use the refunds to lower prices.

After the Supreme Court struck down the tariffs, Trump

ordered new 10% tariffs under a decades-old authority meant to

address a balance-of-payments emergency.

States and private businesses have sued to challenge those

tariffs, which they argue were also illegally imposed.

In addition, the Trump administration has started

investigating unfair trade practices of major trading partners,

a step toward imposing tariffs under a law that has withstood

legal challenges.