(Bloomberg) -- Lawmakers in Montenegro passed a controversial bill on religion that may strip its biggest denomination -- part of the Serbian Orthodox Church -- of vast assets, and fan passions in a region still reeling from ethnic conflict.

The former Yugoslav republic, which joined NATO in 2017 despite opposition from Russia, ignored objections from Moscow and former ally Serbia as it adopted the law, which requires religious communities to prove ownership over temples and land they hold or see the property become assets of the state. At stake are hundreds of churches and monasteries, many built in the Middle Ages.

Opponents of the bill held street rallies in several Montenegrin cities. At least 18 opposition deputies were detained by police for inciting violence early Friday, while hundreds of opposition supporters took to the streets of capital Podgorica and other cities in the Adriatic republic, state broadcaster RTCG reported. Police were also deployed around the parliament to keep angry opposition activists away from the building.

The legislation is backed by the political party of President Milo Djukanovic, who has dominated the tiny Adriatic nation of 620,000 for three decades, evolving over that period from a Communist to a pro-Western leader. His government says it merely aims to sort out ownership rights.

But it has outraged the faithful, clergy and opposition groups, which have held prior protests demanding protection of religious rights and closer ties with neighboring Serbia, from which Montenegro separated peacefully in 2006 after other parts of the former Yugoslavia broke up in bloodshed.

“This law will cause a great rift in Montenegro and a war among its citizens,” opposition lawmaker Slaven Radunovic said during debate over the legislation, which ended in a brawl among parliamentarians as they voted.

Parliament speaker Ivan Brajovic said he banned lawmakers of the pro-Serbian Democratic Front from the legislative body for 15 days for causing the incident.

More than 70% of Montenegro’s population is Orthodox Christian, including a minority loyal to a separate Montenegro Orthodox Church that was formed in 1993 and isn’t recognized by other Christian communities. By contrast, the local branch of the Serbian Orthodox Church controls most temples, including sites that attract hundreds of thousands of pilgrims and resulting revenue.

While Montenegro and Serbia strive to join the European Union, the latter has no intention of being part of the North Atlantic Treaty Organization, which bombed both places in 1999 during the Kosovo War. Montenegro said in 2016 that it had foiled a Russia-backed coup aimed at killing Djukanovic and preventing his nation’s accession to NATO.

Russian Foreign Ministry spokeswoman Maria Zakharova has called for respect of the “legitimate rights” of the largest religious group in Montenegro, and the country’s pro-Serbia clergy has blasted Djukanovic as an atheist bent on a Communist-style crackdown.

Serb leader Aleksandar Vucic has called for restraint to help “preserve peace,” as the only recognized Orthodox Christian group in Montenegro is the branch of the Serbian church.

To contact the reporter on this story: Misha Savic in Belgrade at msavic2@bloomberg.net

To contact the editors responsible for this story: Irina Vilcu at isavu@bloomberg.net, Gregory L. White, Karen Leigh

©2019 Bloomberg L.P.