Sellers of Germany-based staffing firm 7S to ManpowerGroup (NYSE: MAN) claim they are owed an additional $25.0 million plus interest in contingent consideration related to the acquisition, according to a 10-K filing with the US Securities and Exchange Commission.

ManpowerGroup acquired 7S in 2015, but the sellers initiated a dispute on April 26, 2017.

“Under this process, the dispute has been submitted to an arbitration tribunal in Germany,” according to the filing. “We believe no further amounts are due and intend to vigorously dispute their claims in the arbitration.”

ManpowerGroup acquired 7S in September 2015 for total consideration, net of cash acquired, $140.4 million plus contingent consideration of $10.3 million paid in the first quarter of 2017 based on the financial results of the company and other factors. 7S provides human resource services that focus on a number of sectors, including skilled trades, engineering and IT.

Aside from this dispute, the overall merger & acquisition landscape has been growing over the past few years, according to a new report by Staffing Industry Analysts.

Overall, there were 88 publicly announced merger & acquisition deals in 2017, an increase of 28% over the previous year, according to a new report “North America Staffing Mergers & Acquisitions: 2018 Update” by Staffing Industry Analysts. Last year saw the second-highest annual deal volume over the past decade. However, activity still remains below pre-recession levels.