Auburn deputy mayor Salim Mehajer has broken NSW electoral law by failing to reveal fundraising and spending that led to his 2012 election to the council, raising questions about how his campaign was bankrolled.

Three years after Cr Mehajer was elected - and despite hitting him with two penalty notices - authorities remain in the dark about what money he raised, from whom and how it was spent.

Auburn deputy mayor Salim Mehajer arrives at a council meeting in August. Credit:Wolter Peeters

The NSW Electoral Commission confirmed it issued a $1100 penalty notice to Cr Mehajer for his failure to lodge a donations and expenditure declaration for the 2012-13 financial year.

It said it issued a second $1100 penalty notice to Cr Mehajer when he failed to lodge a declaration for the 2014 financial year.