Dear Sandy,
Many learned followers have give you many theoretical and practical information about your problem. Here is mine, with my experience.
1. It is just likely that automation has taken place, which has made the competencies of old workers redundant, which they are not ready to accept, instead, they are just trying to escape job/job responsibility OR there is over staffing which allows them to have leisure.
SOLUTION : If 1st is the case, you can arrange for their training to enhance their skill and efficiency. If second is the case, re-organize your manpower, you can transfer employees from one department to another, and put right man on right job. This will result in more output with lesser number of men.
2. There are instances that old employee enjoy job security which makes them somewhat undisciplined and often they throw their job and responsibility on their juniors. SOLUTION : Organize manpower hierarchy, I mean - one very senior, assisted by a few juniors, juniors assisted by 2 or three new employees as per the requirement of job. Put a quantitative target to be achieved during a given point/period of time. Keep regular monitoring. The results are bound to come.
3. If these things fail, it is very likely that some of the seniors might be enjoying backing of their Controlling Officers or they might be representing Unions. In this case you have to handle the issue intelligently, because one wrong step will raise IR problem issues.
AK Jain