"We did conduct a meeting, but not where we planned," Fotinia Kotelnikova said, adding the city authorities had prevented them from gathering near a statue of Lenin in the main square by the presidential administration building.
Home to most of Moldova's heavy industry, including a steel plant and hydro power station, Transdnestr has been under customs restrictions, which was imposed by neighboring Ukraine at Moldova's request, since March 2006.
The move, which Tiraspol called an economic blockade, has been a serious blow to the ex-Soviet region's struggling economy, causing the halt in deliveries of goods to Ukraine over the lack of an official Moldovan customs stamp.
Kotelnikova said about 150 people had gathered for the rally, much fewer than expected as many supporters had been deterred by the change in venue.
She said a police cordon had also prevented about 50 activists from going to the main police department to demand the release of Communist Party leader Oleg Khorzhan and Nadezhda Bondarenko, a senior party official who was incumbent President Igor Smirnov's rival in the December elections.
Khorzhan and Bondarenko were arrested Sunday when handing out leaflets ahead of the rally and sentenced to three-day's detention as an administrative punishment.
Kotelnikova said the party would make a statement on the arrests Friday and would pass a resolution adopted at the rally to Smirnov.
Smirnov won a landslide victory in the poll and took office for the fourth consecutive time. Moldova and the European Union have not recognized the vote or its result.