Up to 1,000 senior gardaí are considering taking early retirement because of the government's controversial public sector pension levy scheme.

More than 500 gardaí are understood to have already lodged their papers and it is expected that hundreds more will follow suit.

Some gardaí are permitted to retire at the age of 50 but the majority cannot retire from the force until 55. Retirement becomes mandatory for gardaí at 60.

"A lot of officers eligible for retirement are looking at their options. A lot of them are sitting down and doing the calculations and figuring out they'd be better off retiring than taking the cut," said Garda Representative Association (GRA) president, Michael O'Boyce.

"We cannot afford to have a huge loss of experienced officers because of bad policy decisions by the government. We have been contacted by a huge number of our members about this."

At present, the majority of gardaí retire from the force at 60 or a year before. "Often, gardaí retire shortly before they reach 60. It's a case of choosing to retire rather than being forced to. But now, gardaí are considering retiring far earlier. People should not be forced into retirement," added O'Boyce.

Some of Dublin's most senior detectives have already handed in their papers, leaving the force with a dearth of investigating expertise. Detective Superintendent Denis Donegan, who is in charge of the Dublin metropolitan south district, is to retire, as is Detective Superintendent PJ Browne who heads Dublin metropolitan south central region. The man in charge of investigating serious crime in west Dublin, Detective Superintendent Hubert Collins, is also retiring early as is the head of garda crime and security, Chief Superintendent Tim Maher.

A graphic poster campaign depicting gardaí who have received facial injuries in the line of duty was launched by the GRA two weeks ago, as part of a campaign against the public sector pension levy. The image is intended to highlight the dangers officers face and is not a shock tactic, according to the association. The billboard posters show a male and a female officer with serious facial wounds and state: "Gardaí face injuries in the line of duty – they do not deserve pay cuts."

The GRA maintains that the pension levy and the postponement of a 6% pay rise will see many members lose out on about €300 per month. A "withdrawal of labour" has been mooted by rank-and-file gardaí if the government fails to address a number of key issues. Under current legislation, gardaí cannot take strike action.

In 1998, gardaí took unofficial action during its 'blue flu' campaign, which saw members ring in sick in a row over pay. However, GRA president O'Boyce has ruled out the possibility of another 'blue flu' campaign.