Sirisena's allies say the president has deliberately stalled local council polls to buy time as he tries to heal rifts within his own party, an accusation he denies.
The local vote, likely to be in early February, is seen as a crucial mid-term test for Sirisena, who has struggled to hold the raucous ruling alliance together since his election in 2015.
Rajith Keerthi Tennakoon from the non-profit Campaign for Free and Fair Elections said voters were no longer considering this a small local election.
Sirisena has said the election was delayed by nearly two years because authorities had to redraw complex electoral boundaries.
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The clash over the local polls is the latest in a series of disputes within the ruling coalition, formed after Sirisena split his own Sri Lanka Freedom Party (SLFP) and secured support from the rival United National Party.
The allies have since clashed over economic policy and on stalled investigations into corruption under the regime of former president Mahinda Rajapakse, who is also from the SLFP.
The president's own party is split between him and predecessor Rajapakse, who ruled Sri Lanka for a decade and presided over the end of the decades-long civil war.
Rajapakse remains a threat to Sirisena's leadership of the SLFP, wielding considerable influence in Sri Lankan politics.