Minister for Social Protection Joan Burton has denied there has been any change to the eligibility criteria for disability allowances.
Ms Burton said her department was not making it more difficult for people who apply.
Fianna Fáil TD Willie O'Dea said the refusal rate for initial applications for the disability allowance rose from 54% in 2010 to 61% of applications being refused in the first quarter of this year.
Speaking on RTÉ's Today With Pat Kenny, Ms Burton said "nothing underhand is going on".
She said there had been a large increase in the volume of applications for disability allowance, particularly from recipients of other welfare payments, such as jobseeker's allowance, who wanted to transfer.
The minister said there had been "absolutely no change in criteria or conditions".
She said the department is currently changing computer systems dealing with applications, which should be complete by the end of September, and that would improve waiting times for decisions.
The minister said officials in her department are required by law to examine all disability claims in detail to see if they meet criteria.