The Guardian is preparing a lawsuit against online ad tech firm Rubicon Project on the grounds of “non-disclosed buyer fees in relation of Guardian inventory.”

As first reported by Business Insider, and later confirmed by The Guardian, the British publisher is due to file legal papers at the UK High Court’s Chancery Division. Rubicon Project intends to challenge The Guardian’s claim over the recuperation of, what is believed to be, an amount in the single-digit millions.

“We charge buyer fees for certain services we provide and have disclosed that fact publicly, including in our SEC filings, and in client contracts, including a contract we signed with Guardian over a year ago. We split our fees between sellers and buyers, reflecting the value we provide to both,” said Rubicon Project in a statement.

“We believe that the aggregate fees we charge represent the value for our services and are in line with industry practice. The Guardian’s claims amount to a contract dispute, which we will vigorously contest in court.”

Rubicon Project has had it rough over the last six months. In November, following its Q3 2016 financial results, it cut its workforce by 19 per cent – or 125 employees – as part of a ‘comprehensive realignment of the business’. The departures continued last month when seven executives departed the company as part of the continued restructuring. The realignment would start to take shape when it announced a new CEO in the form of former Millennial Media CEO Michael Barrett, and a new look EMEA leadership team earlier this month. While this was all going on, it has also seen its share price fall by nearly 70 per cent in the past year.