China's government is reportedly cracking down on exports into Hong Kong, banning items that could be used for protest.
Courier companies on the mainland have been advised to halt delivery of black clothing, among other items, the South China Morning Post reports.
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A Beijing based courier worker told the South China Morning Post black clothing cannot be shipped to Hong Kong and items are taking two days longer than usual to arrive at their destination.
A recent post on online shopping platform Shopify said users had been having issues with sending the clothing.
"China has put out an official [Public Service Announcement] to all courier services to stop picking up any clothing items that are considered black or even navy blue for an undisclosed amount of time."
A notice issued to Guangdong courier company PHXBUY in July said yellow helmets, yellow umbrellas, flags, flagpoles, poster banners, gloves, masks, black T-shirts, metal rods, fluorescent tubes, bludgeon clubs could not be sent.
Another notice sent to a different courier company in September had an even longer list of banned items, including helmets, speakers, walkie-talkies, drones and goggles.
Protests have overwhelmed Hong Kong since July when demonstrations began in response to a proposed extradition bill.
The bill has since been withdrawn but protesters are continuing to fight what they see as China's increasing influence in Hong Kong.