The bitter battle between private betting companies and EU countries that operate state-owned gaming systems took a new twist on Tuesday when a senior adviser at Europe’s top court said that it was up to the local courts to decide whether Portugal acted legally when it extended its gambling monopoly to internet-based betting.

An advocate-general at the European Court of Justice said that the Portuguese decision to prohibit online gaming operators based outside the country from offering online services could be legal if it met certain conditions.