The railway company had shut some stations in the run-up to rallies in various parts of the city in recent weeks – even when the demonstrations were sanctioned by the police.
But no such closures have yet been announced before a 7pm rally at Tamar, organised by the Civil Human Rights Front.
Several station exits were closed though at both the Admiralty and Causeway Bay stations.
The corporation warned that measures, such as closing stations or trains skipping certain stops, could be implemented without prior notice “for safety reasons”.
The railway firm has become a target of hardline anti-government protesters, who accuse it of siding with the police over the current turmoil.
Trains carrying only riot police, and pictures of officers using closed stations as rest stops have fuelled anger against the corporation, which has seen repeated acts of vandalism in recent weeks.