HONG KONG, July 4 (Reuters) - Beverage maker Vitasoy (0345.HK) has become the latest target of Chinese netizens" calls for a boycott after an employee circulated a memo online offering condolences to the family of a worker who had stabbed a Hong Kong police officer. In a statement on the Chinese social media platform Weibo on Saturday, Vitasoy said a staff member had circulated a memo that it described as "extremely inappropriate" without authorisation, and the company reserved the right to take legal action. The memo offered condolences to the family of a 50-year-old Vitasoy worker who had stabbed a police officer, 28, and then killed himself on Thursday, the anniversary the former British colony"s return to Chinese rule, media outlets reported. read more "What this employee wrote should not have been made public and should not have been published internally," Vitasoy said. "Vitasoy Group sincerely apologises for any troubles or grievances this has caused. We support Hong Kong"s long-term prosperity, stability and development." Police have described the stabbing as an attempted murder. The officer"s condition has improved from critical to serious. The worker"s memo triggered a flood of online calls for a boycott of Vitasoy, which gets two-thirds of its revenue from mainland China. The hashtag "#Vitasoygetoutofthemainland" has garnered almost 100 million views. Hong Kong authorities warned on Sunday that advocating for people to mourn for the attacker was no different from "supporting terrorism" and criticised parents who took children to mourn him. The Police National Security Department said it had taken over the case and initial investigations showed it was a "lone wolf-style act of domestic terrorism, in which the attacker was believed to be radicalised by myriad fake information." It warned members of the public "not to tolerate or glorify violence." A 20-year-old woman and a 26-year-old man were arrested on suspicion of inciting others to commit murder, as well as arson and seditious intention, said police Superintendent Wilson Tam. Tam did not specify whether the arrests were related to the stabbing, telling a news conference only that the pair were suspected of posting messages on social media on Friday. One of the messages incited people to kill police, he said, adding that more arrests could not be ruled out. On Friday, people went to the scene of the attack, some with children, to pay their respects to the attacker and lay flowers. Mainland actor Gong Jun, who previously endorsed a Vitasoy lemon-flavoured drink, announced late on Friday he was ending commercial cooperation with the company, said Global Times, a tabloid published by the ruling Chinese Communist Party"s official People"s Daily newspaper. His announcement followed that of another mainland Chinese actor, Ren Jialun, who said he was also ceasing co-operation with Vitasoy, the newspaper added. Fashion retailer H&M (HMb.ST) said on Thursday its sales took a hit in China after its concerns over alleged human rights abuses in Xinjiang led to a social media-inspired boycott by shoppers. read more