I get a syntax error running your code:

$ perl label.pl 
syntax error at label.pl line 3, near "L001:"
Execution of label.pl aborted due to compilation errors.
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But I'm not really sure what the problem is. Maybe labels are only legal on blocks? But adding blocks only makes the error weirder:

syntax error at label.pl line 3, near "L001"
"use" not allowed in expression at label.pl line 3, near "{ "
Execution of label.pl aborted due to compilation errors.
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-sam