LONDON (Reuters) -Online fast-fashion retailer Shein has dropped Brunswick and FGS, two communications firms that were supporting its push for a London initial public offering (IPO), a source familiar with the matter confirmed on Friday, in the latest sign the flotation is not going to plan.

Steep tariffs on Chinese goods imposed by U.S. President Donald Trump, along with the removal of a duty exemption on low-value ecommerce packages, are challenging Shein's business model, which relies on shipping clothes from factories in China directly to customers around the world.

Brunswick was assisting with media relations while FGS was tasked with government relations, and both of their contracts with Shein ended on April 30 and will not be renewed, the source said. The news was first reported by The Times.

Brunswick and FGS both declined to comment. Shein did not immediately reply to a request for comment.

Singapore-headquartered Shein has secured approval from Britain's financial regulator for its IPO but is still awaiting the green light from China's regulator which it also needs in order to go ahead, Reuters reported last month.

Shein had aimed to complete the listing in the first half of this year, but market turmoil caused by Trump's tariffs and retaliation from China is likely to delay the IPO to the second half, sources have said.