The incident took place on Thursday. The two sisters, however jumped out of the moving auto, a senior police official said.
According to the complaint, one of the sisters aged 13 was along with her elder sister (16), came to a hotel where their mother was working, to meet her for some work, the officer added.
While they were returning home to Ulhasnagar in an auto-rickshaw, its driver asked them for the cell number of their mother.
He threatened them with dire consequences and took the auto in another direction than proceeding towards their home. He tried to abduct and molest them, but the younger sister jumped out of it, he said.
A case under relevant sections of the Indian Penal Code and Protection of Children from Sexual Offences (POCSO) Act was registered, he said, adding a probe was on.