New government regulations on corporate accountancy have forced many bourse-listed companies to switch accountants, according to a report by research group BreakThrough Solutions released on Tuesday.

BT Solutions said that analysis of annual reports revealed that 37 of the 50 biggest Amsterdam listed companies have switched accountants since 2014. By tradition, the bourse companies employ the services of the big four accountancy firms, PwC, KPMG, Deloitte and EY.

EY has emerged as the overall winner by a fat margin last year, with a 40% share of the listed company market, up from 18% in 2015.  EY picked up the accounts of 10 companies including Shell, Philips and ABN Amro and last year controlled the books of 18 listed companies, earning an audit fee of €109m, the report said.

PwC was the biggest loser last year as clients moved and fees were reduced to €54m (€94m). KPMG and Deloite were in calmer waters. KPMG booked audit fees of €60m, down €6m from 2015. Deloitte registered audit fees of €53m compared with €62m in the previous year, the report said.

The new rules compel large companies to change their accountancy firms at least once every 10 years starting in 2016. Many tenders went out in 2013 making waves throughout the normally staid Dutch accountancy world.