Ryanair Holdings Plc is forcing investors who aren’t European Union citizens to sell any shares purchased after Jan. 1, in a reminder of the lingering constraints on investors tied to the Brexit split. 

Non-EU citizens have been barred from buying stock in the Irish discount airline since the U.K. left the bloc at the start of the year. When such purchases have been made, Ryanair has restricted the shares and told the owners to dispose of them, the company said in a statement Wednesday. 

Some haven’t complied, and as a result, Ryanair said it’s initiated the forced sale of about 1 million ordinary shares. The company said it may have to do further sales “from time to time” to stay within EU rules. The current investors will receive the proceeds. 

Ryanair instituted ownership restrictions on non-EU members, including a voting-rights suspension, last year as Brexit approached. Britons who already owned shares of the Dublin-based company were allowed to keep their holdings, but no further purchases were permitted.

Until the split, British citizens were counted as EU-based under rules that require companies to be majority owned and controlled by members of the bloc.