It does not complain about that. Here is my SSCCE showing as such:

$ cat x.pl 
#!/usr/bin/env perl
use strict;
use warnings;
use utf8;

sub foo {
    my %arg = @_;
    print "Woo!\n";
    return;
}

foo (z => 3);
$ perlcritic --stern x.pl
x.pl source OK
$
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This suggests that the cause of its complaint (if any) is in the code which you have not shown, such as if you have done something in the sub before that line and hence that line is not "first".

> you have done something in the sub before that line and hence that line is not "first"

Thank you hippo! That is exactly the case. Why is that not a PBP? I have good reasons for putting code before dealing with parameters in subs, like using IPC::Cmd to check if we can run an executable:

sub something {
  return 'oops' unless can_run('something');
  my %arg = @_;
  ...
}
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