A watchdog plans to use new powers for the first time to investigate how a Stormont department handles Personal Independence Payment (PIP) benefits.
PIPs replaced the Disability Living Allowance (DLA) benefit in June 2016.
Public Services Ombudsman Marie Anderson can investigate if her office suspects "systemic maladministration".
The Department for Communities, which administers PIP, told BBC News NI that only six out of 160,000 decisions have been referred to it by the ombudsman.
In a statement, the ombudsman said she has written to the department's top civil servant "stating that since June 2016 there have been a significant number of complaints about PIPs to her office".
Ms Anderson also pointed out that a "high number" of the department's decisions on PIP applications have been subsequently overturned by an appeal tribunal.
The ombudsman said she was satisfied that the criteria has been met for her to carry out what is known as an "own initiative" investigation.
The ombudsman's office regularly deals with complaints from the public on a wide range of public services.
But, under new powers granted to watchdog in 2016, Ms Anderson is entitled to investigate suspected maladministration in public services even if her office has not received a single complaint.
The proposed PIP investigation is the first time that the ombudsman will use her "own initiative" investigatory powers.
She does not need the department's permission to begin the investigation, but her spokesman said they will await a response from civil servants before proceeding with the planned inquiry.
'Exhausted' complaints procedure
In a statement, the Department for Communities noted the proposed investigation but said its staff were "operating within the appropriate statutory mechanisms".
"It is administered no differently from the rest of the United Kingdom, with the exception that, in Northern Ireland, welfare supplementary payments are available for those who are adversely impacted by welfare changes," the department added.
BBC News NI asked the ombudsman's office how many PIP complaints it has received to date.
A spokesman confirmed the office has received 19 PIP complaints since June 2017, but pointed out that the ombudsman can only act on individual grievances when the complainant has "exhausted" the complaints procedure of the organisation which provided the service.
He highlighted the number of successful PIP appeals cited in a recent Northern Ireland Audit Office (NIAO) report, which looked in detail at what happened to 140,000 PIP decisions made between June 2016 and September 2018.
Almost a quarter of all PIP decisions (24%) were challenged by claimants and more than half (55%) of cases that went to an appeal tribunal were overturned.