to be on (someone's) case
Explanation:
on (someone's) case
Persistently nagging or urging someone to do something
http://www.thefreedictionary.com/on (someone's)+case
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Note added at 1 hr (2011-08-01 20:31:48 GMT)
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Ex.:
At work, slackers will often find their boss is on their case, making sure they do a good job.
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Note added at 10 hrs (2011-08-02 05:44:21 GMT)
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Also consider:
be hard on -- Deal severely with, cause damage to. For example, He asked the teacher not to be too hard on those who forgot the assignment
http://idioms.yourdictionary.com/hard-on
|   Andrei Yefimov
Ukraine
Local time: 04:24
Works in field
Native speaker of:  Ukrainian, Russian
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The translation workplace 
peer agreement (net): +5