If a service agent asks for Aadhaar mandatorily, then as a beneficiary, citizens have no option but to get an Aadhaar number.
The new Aadhaar Act does not incorporate a categorical clause saying Aadhaar will be voluntary, or that it will NOT be made mandatory. Instead, it broadens the scope of Aadhaar. In parliament in March, Finance Minister Arun Jaitley said the Aadhaar Act will allow the government to ask a citizen to produce an Aadhaar number to avail of any “government subsidy”.

But section 7 of the Bill is phrased more broadly, and refers to not just subsidies but any “subsidy, benefit or service” for which expense is incurred on the Consolidated Fund of India, or the government treasury. This is a sweeping scope, and we are seeing the impact in the notifications issued by the government in the past few weeks: government is demanding Aadhaar, or proof of enrolment in Aadhaar, from everyone from trafficked women seeking assistance to children in government schools for getting their school meals.
Section 7 of Aadhaar Act says:

“Provided that if an Aadhaar number is not assigned to an individual, the individual shall be offered alternate and viable means of identification for delivery of the subsidy, benefit or service.”

In the recent notifications, Government has got around the proviso for an "alterntate" ID, by making the proof of applying for enrolment in Aadhaar itself as the alternate ID it will recognise! Talk of arm-twisting citizens.

Aadhaar law allows private companies too use it, such as an application used by a company doing authentication for those applying to jobs, even if a prospective employee or tenant shares his/her Aadhaar number, it does not amount to free consent since getting a job or a house may hinge on providing the Aadhaar number.