European Union officials fired an opening salvo on Thursday in a “Brexit”-related dispute that could threaten London’s status as the undisputed financial capital of Europe and affect hundreds of trillions of dollars’ worth of financial products.

In the course of a series of proposed technical changes, the European Commission, the executive arm of the 28-nation bloc, hinted that it may seek a more centralized role in supervising the complex financial contracts known as derivatives when they are denominated in euros. It also suggested that it could institute requirements that clearing houses, which act as middlemen in derivatives transactions, be located within the European Union.

Those rules, if enacted, could force clearing houses for derivatives to be regulated by European authorities even after Britain leaves the bloc, or to relocate part of their operations in order to avoid losing business to competitors.

The proposals, released in briefing documents on Thursday, form part of an increasingly heated negotiating process over Britain’s withdrawal from the European Union. Tensions have played out in recent days in newspapers in Britain and on the Continent.