A representative for the independent Center for Election Monitoring, Anar Mammadli, told AP that election workers at some polling places were not marking voters' thumbs with invisible ink that could be detected by an ultraviolet monitor. The invisible ink is meant to prevent voter fraud.
Mammadli said there were also discoveries of ballots that had been filled out before the vote.
Opposition leader Ali Kerimli said his Popular Front of Azerbaijan had recorded what he called "numerous violations."
Kerimli said the opposition will call for protest against the election results in the event of widespread fraud.
"We have plans in place so that if there is widespread fraud, we will certainly call on the people of Azerbaijan to protest against falsified results ," Reuters quoted Kerimli as saying . " And we will start our protests from 8 November. These protests will be peaceful. We want to have legal action. And will do our best not to hand the authorities an excuse to use violence against us."
There's been no comment from the authorities about the allegations of violations. Earlier however, President Ilham Aliyev said he was confident the elections will meet democratic standards. Aliyev, whose Yeni Azarbaycan Party dominates the outgoing parliament, was speaking to journalists while casting his vote in Baku.
More than 1,500 candidates are competing for places in the 125-seat Milli Majlis. Election officials said turnout had reached more than 18 percent four hours after polls opened.
RFE/RL's complete coverage of the November 6, 2005, legislative elections in Azerbaijan and their aftermath.
Timeline: How The Elections Have Unfolded
A photo gallery of the Azerbaijan opposition protests in Baku on November 9, 2005.