An MLA has said any DUP move to block an Assembly bill banning dual mandates would set a dangerous precedent.
Dawn Purvis' bill to stop MLAs also being councillors has passed several legislative stages.
However, she has warned that she believes the DUP will move a "petition of concern" to stop it becoming law.
The DUP said that it was considering the matter because of the assembly's failure to "accept any of our reasonable amendments".
The DUP amendments would have delayed a ban until 2014 while ensuring that any MLAs who were also councillors in the intervening period would only have be paid for one job.
Ms Purvis' bill would end dual Assembly and local government mandates by the time of the council elections next year.
A number of MLAs, including several from the DUP, have already resigned their council seats.
Ms Purvis said the petition of concern, which means that a bill has to be supported by a majority of both nationalists and unionists, was supposed to ensure that legislation did not unfairly disadvantage one community.
She said: "It sets an extremely dangerous precedent. The DUP is using the procedure, which should be used with careful consideration, to support their own interests as a political party."
She added that it was "inappropriate and unfair" for one person to hold two elected positions at the same time.
"I would call on Peter Robinson to support the final passage of the bill - after all he gave a commitment to bring an end to this practice of holding dual mandates."
A DUP spokesperson added that it "will not stand in the way of any party wanting to voluntarily reduce their dual mandates."