(Bloomberg) -- The European Union’s top markets regulator plans to close a loophole in the MiFID II rules that can put the bloc’s stock exchanges at a disadvantage to foreign competitors.

Firms including Cboe Global Markets Inc. and Aquis Exchange Plc had prodded regulators to fix a rule that can allow exchanges outside the EU to price stocks more competitively than those in the bloc under the revised Markets in Financial Instruments Directive. The so-called tick-size rule has benefited exchanges such as SIX Swiss Exchange AG.

“These specific cases where EU trading venues might be subject to minimum tick sizes larger than those applicable on non-EU venues may have the unintended result of putting EU trading venues at a competitive disadvantage,” ESMA Chairman Steven Maijoor said in a statement on Friday.

Alasdair Haynes, chief executive officer of Aquis, said he’s “delighted to see the loophole being closed and that no competitive advantage is given to one exchange.” A spokeswoman for Cboe didn’t immediately respond to a request for comment.

The MiFID II tick-size rules are an attempt to level the playing field between trading platforms by regulating the minimum price increment they can use. Under the rules as they stand, only transactions on EU exchanges are figured into this calculation. ESMA’s proposal would factor in the average daily number of transactions for stocks that have their main pool of liquidity outside the EU.

Cboe and Aquis began pushing ESMA to change the rule even before the MiFID II start date on Jan. 3. In January, they said the rules were discouraging some investors from trading on their platforms, and that they’d align their tick sizes with the Swiss market in some cases to remove the impediment.

(Updates with Aquis comment in fourth paragraph.)

To contact the reporter on this story: Viren Vaghela in London at vvaghela1@bloomberg.net

To contact the editors responsible for this story: Ambereen Choudhury at achoudhury@bloomberg.net, Patrick Henry, Vernon Wessels

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