"These monitoring groups are biased. They are highlighting issues against the government but turn a blind eye to others," Anura Yapa, petroleum minister and the ruling party's general secretary said.
The ruling party was irked by action of the People's Action for Free and Fair Elections (PAAFREL), the leading polls monitoring group.
PAFFREL has written to the chairman of the state passenger bus agency to stop the abuse of the state-owned buses by the ruling party for election propaganda work for the incumbent Mahinda Rajapaksa.
Yapa said the polls monitors were making false allegations.
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The presidential election is to be observed by over 100 international observers, election secretariat officials said.
The international observers will arrive in the island on December 27.
Some 14 million people are eligible to vote in the country's election.
Rajapaksa - who was elected in 2005 and 2010 - is seeking re-election amid signs of a drop in popularity and demands for his powers to be curbed.
Seeking a record third term after he pushed through changes to the constitution, Rajapaksa has ordered snap polls on January 8.