Turkish lawmakers voted early Thursday morning to amend their country’s Constitution to allow observant Muslim women to wear head scarves at universities. The controversial measure, which requires a two-thirds majority for final passage, won preliminary approval on a secret ballot by a vote of more than 400 in favor and about 90 against after a marathon parliament session that had begun 12 hours earlier, according to news reports.

The result had been expected since the governing party and the main opposition party announced late last month that they had reached an agreement to rescind the head-scarf ban, but the measure’s likely passage has only inflamed debate and tensions around the issue, which has long been a lightning rod of controversy between secularists and observant Muslims. Last Saturday, more than 100,000 opponents of the ban’s removal — most of them women — marched in protest in Ankara, the Turkish capital.

Turkey’s Higher Education Council, a staunchly secularist government body that oversees all of the country’s universities, has backed the head-scarf ban since its introduction, in the early 1980s, and a group of state university rectors last week condemned the move to rescind the ban as a weakening of Turkey’s constitutional commitment to secular education.

Many academics, however, support allowing observant Muslim women to wear the head scarf as a profession of their religious faith. A newspaper in Turkey reported that more than 3,000 people had signed a declaration in support of head-scarf freedom in universities since Friday. Some signers told the newspaper, Today’s Zaman, that they had come under pressure for expressing their views.

Another, final round of voting on the head-scarf measure will take place on Saturday, but at least one opposition party has vowed to challenge any changes to the Constitution in court, and many university officials have said they do not expect the ban to be lifted in practice anytime soon. —Aisha Labi