Special constables gave up 7,110 hours of their spare time to help South Yorkshire Police last month.
Specials are volunteers who have the same powers as regular officers.
They wear the same uniform and have the power of arrest.
South Yorkshire's former Police and Crime Commissioner, Shaun Wright, made it a priority to boost the number of Specials when he was in post to help fill the gaps left by funding cuts.
But Neil Bowles, chairman of the South Yorkshire branch of the Police Federation, said he would rather there were more regular officers.
“Volunteering as a concept has had a long history in this country. It is beneficial for the individual, organisation and society as a whole," he said.
"The Special Constabulary fits that concept well - members of the public volunteering to police their own communities; the public are the police, and the police are the public.
"However specials were always around to complement the regular officers and not replace them. They do not have the required time to train and learn by experience that a full timer has. Regular constables train for their first two years before they have their appointment confirmed.
"Over 7,100 hours worked by Special constables in one month is laudable and my colleagues will be very grateful for their assistance, but that works out at nearly 45 full time officers work. Is this still complementary to the service?
"As a staff association we want to see more officers employed to keep the public safe. Well trained and well motivated officers will provide the service that we all want to provide, but cannot achieve at this time.”
Superintendent Neil Thomas, of the South Yorkshire Special Constabulary, said: “South Yorkshire Police currently has 338 Specials working alongside regular officers.
"Our Specials provide a vital resource that delivers additional capacity and capability to our frontline service.
“The level of commitment and the hours provided by our Specials is something that South Yorkshire Police is rightly proud of and they play a key role in providing our visible presence within the communities of South Yorkshire.”
A South Yorkshire Police spokesman said: "Specials come from all walks of life - they are teachers, taxi drivers, accountants and secretaries, or from many other careers - and they volunteer for a minimum of 16 hours a month, forming a vital link between the regular police and the local community.
"As a Special constable you are in a great position to help the local community and make it a safer place to live.
"You will get a feeling of achievement and accomplishment at having done something to help others, while supporting regular officers and contributing to the local community.
"Becoming a Special will help you to discover a lot about yourself, and you will learn just how much you are capable of.
"Joining the Specials opens up a world of opportunity for personal and professional advancement. Undergoing the training and then going out on patrol makes a welcome break from day-to-day life, bringing excitement and challenge with every day you volunteer."
An information evening will be held at Barnsley College's University Campus, Church Street, on Monday, September 12 from 6pm.