The animal welfare charity says 19 past and 22 present employees have been affected by payroll errors.

The organisation became aware in June 2017 of potential issues and brought in global consultancy firm Herbert Smith Freehills to examine the problem.

"Following detailed analysis, the results indicate that a total of 19 past and 22 present staff members out of 531 current staff members, were affected," RSPCA NSW said in a statement on Tuesday.

"This equates to $112,262 in relation to current employees and $10,412 in relation to past employees."

The charity said it has since gone to "significant effort to review every personnel file for each of our staff members to ensure that pay rates, classifications, allowances and other benefits are consistent with the relevant awards or agreements and the individual staff member's letter of offer".

A former employee who spoke to News Corp Australia said she believed "a lot" of employees were not aware of their entitlements.

Federal Labor frontbencher Tony Burke said "every Australian worker has a right to be paid what they're owed".

"All employers - whether they're multinational giants or not-for-profit charities - must pay their staff properly," he said in a statement.

It's understood the charities watchdog - the Australian Charities and Not-for-profits Commission - has been made aware of the RSPCA's payroll issue.

Australian Associated Press