The union of more than 300 sellers on Rakuten alleges that the company is abusing its dominant position in forcing them to shoulder costs for free shipping on all orders exceeding 3,980 yen starting March 18, calling it a violation of the antimonopoly law.
 

They also requested the antitrust watchdog to investigate cases in which some sellers say they were forced to use Rakuten's mobile payment system and shoulder its commissions, or that they were unfairly fined by Rakuten for minor violations of its rules.
 

The union said it "cannot tolerate repeated unilateral rule changes that are detrimental to merchants."
 

A Rakuten executive said the company will consider its response to the matter, adding, "We will continue our efforts to gain the understanding of sellers."
 

The commission, which has been stepping up oversight and regulation of Rakuten and other large online businesses, is expected to conduct investigations based on the antimonopoly law.
 

At present, the roughly 49,500 merchants on Rakuten's online shopping mall independently set shipping fees for each item, with some providing free shipping and others offering no such services.
 

Small-scale sellers say they cannot survive without passing on shipping costs to customers, and that the free shipping policy would make them less competitive than major merchants.
 

Rakuten officials have argued that a free-shipping service for a minimum purchase amount would increase the number of customers and the amount of purchases, benefiting merchants in the long term.