A number of Turkish universities have defied a new law allowing women students to wear Islamic headscarves.
Local media reported students wearing headscarves being turned away from some premises - although exceptions included the Bosporus University in Istanbul.
It follows constitutional amendments passed by a huge majority in parliament and signed into law last week.
Opposition parties want the law quashed amid fears that Turkey's strictly secular state could be undermined.
The main opposition party has said it will ask the Constitutional Court to quash the law, which it says threatens the division between religion and state.
'Duty to obey'
One of the amendments states that everyone has the right to equal treatment from state institutions and the other that "no-one can be deprived of [his or her] right to higher education".
Yusuf Ozcan, head of the Higher Education Board, said in a statement at the weekend that university presidents "have the duty and responsibility to adjust practices in line with the constitutional amendment".
Local media reported three universities in Istanbul, two in Ankara and five in the western city of Izmir have maintained the ban, along with universities in six other cities.
Others have started to allow headscarves on campus.
Reports say some students were angered by guards asking them to remove headscarves before entering campuses on Monday.
But Reuters reports that others obliged without protest.
"I will follow whatever the rector says," said a student at Ankara University. She said she was "thinking of taking it off" to get inside the campus.
A strict headscarf ban had been in force in Turkish universities since 1997. The ban came after the staunchly secularist military exerted pressure to oust a government it saw as too Islamist.
The changes state that only traditional scarves will be permitted in universities, tied loosely under the chin.
Headscarves that cover the neck are still banned, as is the chador and the all-enveloping burka.