WASHINGTON, May 4 (Reuters) - The U.S. Customs and Border Protection (CBP) agency said on Monday it now estimates the first electronic refunds from U.S. President Donald Trump’s tariffs deemed illegal by the Supreme Court will start as soon as May 12, a day later than an earlier estimate.

The estimated start date for Automated Clearing House (ACH) payments was disclosed in a message to shippers announcing the availability of status reports that allow claimants to monitor the processing status of their refunds.

In a Court of International Trade order last week, the agency was expected to start refunds around May 11. No reason was given for the date change.

Up to $166 billion of CBP collections from Trump’s tariffs imposed under the International Emergency Economic Powers Act are subject to CBP refunds. The Supreme Court ruled that Trump overstepped his authority in using the 1977 sanctions law to impose tariffs.

(Reporting by David Lawder: Editing by Neil Fullick)