Langham said the lawsuit from Ariadne Capital – the venture capital firm founded by high-profile entrepreneur Julie Meyer, co-founder of the networking club First Tuesday – came after Lansons chased up £70,000 it said it was owed in unpaid invoices.
The lawsuit from London-based Ariadne accused Lansons, which worked with the firm for almost two years, of a "botched attempt to improve a Wikipedia entry in a campaign that did its reputation more harm than good".
According to the lawsuit, reported by Bloomberg, a Lansons employee emailed Wikipedia asking for details of Ariadne to be updated on Wikipedia. The email was then published on the page, along with a message that the contents were disputed.
Ariadne claimed this led to accusations the company had tried to "manipulate its own entry" and caused "further negative updates on Wikipedia".
The lawsuit says Ariadne is claiming damages of £100,000 from Lansons, which is counter-suing its former client for £76,000 in unpaid invoices.
According to Bloomberg, Lansons argued in defence papers that any problems with the PR campaign were caused by Ariadne being "insufficiently appealing to the media" and by the fact Meyer "has a poor reputation in parts of the investment industry".
In a statement provided to PRWeek, Langham said: "Ariadne repeatedly praised Lansons’ work and gradually got behind paying our bills. When asked, Julie Meyer always promised that she would pay all bills in full. Eventually, when the outstanding amount reached £70k we suspended all work for them.
"Ariadne then falsely claimed to have been dissatisfied for a while and out of the blue raised the Wikipedia issue. They then hit us with a joke lawsuit.
"I have never had a client behave like Ariadne in 27 years in business. However, we expect, eventually, that all of our outstanding invoices will be paid in full."
The London Evening Standard reported in February that Ariadne had been involved with a number of lawsuits in recent years. Last year Start Up Loans, the business then led by former Dragons' Den star James Caan, won a case against Ariadne to reclaim £50,000 under a scheme to help entrepreneurs.
PRWeek asked Ariadne for comment but received no reply at the time of publication.
However, Bloomberg reports that, according to the lawsuit, the firm accused Lansons of failing to generate sufficient press coverage and said meetings with journalists were "random". Ariadne stopped paying its £6,000-a-month retainer when it believed that the agency "was not doing any discernible work".
The case raises the issue of the difficulties PRs can face when trying to influence what is published on Wikipedia. The online encyclopaedia allows anyone to attempt to access or change what is published, although editors monitor submissions.
In 2011, Bell Pottinger was criticised following accusations of extensive manipulation of Wikipedia entries from anonymous accounts linked to the agency. The Independent and the Bureau of Investigative Journalism claimed that Wikipedia entries were amended by accounts linked to Bell Pottinger for clients including former Zambia president Rupiah Banda and the Central Bank of Sri Lanka.
Wikipedia founder Jimmy Wales told the BBC at the time that he was "highly critical of their [Bell Pottinger's] ethics".
Lord Bell, who at the time was chairman of Bell Pottinger’s then owner Chime Communications, later accepted an offer from the Wikipedia's founder to provide training to his employees over the ethical use of the service.
Last September, the CIPR warned PRs they had "absolutely zero to gain" in subverting the rules around editing Wikipedia articles on behalf of an employer or client. That came after the Wikimedia Foundation, which operates Wikipedia, announced it had blocked 381 accounts for so-called 'black hat' editing on the English-language Wikipedia.