“The trader involved had all along been failing to provide authentication after repeated demands during the customs investigation to prove the masks supplied comply with the labelled claims. Arrests were made accordingly for suspected violation of the TDO,” the Customs and Excise Department said in a statement.

Among words on the packaging were “Not made in China” and product performance standards such as “ASTM Level 1” and “fluid resistance”.

Officers raided the party’s registered address in San Po Kong on Friday, seizing 935 boxes containing a total of 32,725 masks with an estimated market value of about HK$93,500 (US$12,000).

Demosisto hit out at the operation as political suppression last week, saying customs had warned that the “Not made in China” claim, which was printed prominently on the box, should not be made if the products were manufactured in Hong Kong, Macau, the mainland or Taiwan.

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The party said it had not announced where the goods were produced, but it did not elaborate on customs’ other allegations.

Many people in Hong Kong had struggled to buy masks to guard against the spread of the coronavirus.

The sale of the masks was launched last month when the party said it had sourced more than 1 million pieces.

The first batch of 350,000 were sold at cost price, HK$100 (US$12.90) for a box of 35 masks, to businesses in the so-called yellow economic circle, stores that publicly supported the anti-government protests that had rocked Hong Kong since last June.

A customs statement on Monday dismissed suggestions that its operation was politically motivated.

“Customs strongly condemns any false accusation maliciously alleging that its law enforcement action against the trader is ‘political repression’,” it said.

It said its ‘Guardian’ operation, which has been running since January, aimed to ensure that common protective items available for sale in the market complied with the law.

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Law enforcement action would continue to be taken if any suspected violation was found, it added.

Demosisto said on Monday the authorities had acted twice against it in a week, showing that the Chinese Communist Party had “never allowed them to gasp for air”.

“Hongkongers should not be intimidated by political repression when the city is facing a crisis,” it said, referring to Beijing’s proposed national security law for Hong Kong. “But [we] have to grow stronger as we battle along.”