The EU is insisting on a "level playing field" as part of the Brexit negotiations. In other words it is trying to prevent the UK from operating as an independent country in all respects, with its own taxation policies and other frameworks which would make the UK a more competitive country than those in the EU.
What could be a more obvious lack of a level playing field than that of UK businesses being forced to compete with businesses in countries with a minimum wage being 1/5th that of the UK? That is the current situation whilst the UK is still in the EU. When the UK leaves, it will still have this un-level "playing field".
In addition companies operating in one country can make royalty payments to parent companies overseas, enabling them to shift profits out of countries with higher corporation tax rates.
In 2016 the EU Commission ruled that Ireland had given the US multinational Apple illegal state aid by allowing it to pay an effective 1 per cent corporation tax.
“These practices undermine fairness and the level playing field in our internal market, and they increase the burden on EU taxpayers,” said EU tax commissioner Pierre Moscovici.
Multinational companies shifted profits through Ireland – an accounting technique designed to avoid corporation tax - equivalent to almost a quarter of the country’s GDP between 2010 and 2015.
https://www.independent.co.uk/news/b...-a8244456.html