Greece has imposed limits on an Islamic legal system established after the break up of the Ottoman empire, making it optional for the regional minority that benefits from the code.

The Greek parliament on Tuesday set down new guidelines on the practice of Islamic sharia law in family disputes. Religious courts that provide for the nearly 120,000-strong Muslim minority in the region of Western Thrace will in future only be able to rule on family law matters such as divorce, child custody and inheritance. All parties must consent to use the procedure outside the secular courts system.

The change to the law comes as the European Court of Human Rights (ECHR) is expected to rule later this year on a case that could have been embarrassing for the Greek government.

A 67-year-old widow, Hatijah Molla Salli, from the city of Komotini in Western Thrace filed a complaint against Greece over an inheritance dispute with her late husband's sisters.

Greece’s leftist prime minister Alexis Tsipras immediately called the vote an “historic step” as it “extended equality before the law to all Greeks.”

The changes come as Greece struggles to accommodate rapid change in its demographics as the fate of tens of thousands of refugee and asylum seekers hangs in the balance. Changes in the system are highly sensitive as the compulsory system emerged from the treaties that saw the establishment of modern Turkey.

The issue has its origins in the period after the First World War, and treaties between Greece and Turkey that followed the collapse of the Ottoman Empire.

The 1920 Treaty of Sevres and the 1923 Treaty of Lausanne stipulated that Islamic customs and Islamic religious law would apply to Muslims who suddenly became Greek citizens. Most still live in the Thrace region, a largely impoverished strip of land in the northeast bordering Turkey.

The parliament’s move comes as the ECHR is expected to rule in February on Mrs Salli's case. When she appealed to Greek secular justice, she initially won her case. But the Greek supreme court in 2013 ruled that only a mufti had the power to resolve Muslim inheritance rights.

“The government is only acting to prevent condemnation by the court, which, as everyone knows, is inevitable,” Mrs Salli’s lawyer, Yannis Ktistakis has said.

Greek leaders said the current changes reflected the modern pressures of European integration -- adding that all citizens should have the right to use the established court system.

Constantine Gavroglou, minister of education and religious affairs, said the current rules stemmed "from policies that were hostile toward the minority and sought to create second-class citizens."

"This is not just a technical adjustment, it's a very important day for parliament ... because of the broad support that is key when addressing issues of democracy and people's rights," Mr Gavroglou said.

However Greece is not the only European country that offers an Islamic justice system within the overall legal framework. Britain has for years allowed sharia-based tribunals to adjudicate in Muslim family matters.

The issue is complicated by still-tense relations between traditional rivals Greece and Turkey.

Ankara takes a close interest in the Muslim community – which it sees as Turkish – and frequently makes representations on complaint from individuals to Athens.

The Greeks consider such contacts as interference in their country's domestic affairs.