Change the number of regexes that you need to one via Regexp::Assemble reducing the inner loop from many to 1?

use Regexp::Assemble;
 
my $ra = Regexp::Assemble->new;
$ra->add( q{Sarnia Employees' Bargaining Association} );
$ra->add( q{Sarnia Municipal Administrative Employees' Assn} );
$ra->add( q{Sarnia Police Association} );
$ra->add( q{Sarnia Professional Fire Fighters} );
print $ra->re;
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which yields a single regex:

(?^:Sarnia (?:(?:Municipal Administrative Employees' Ass|Employees' Bargaining Associatio)n|P(?:rofessional Fire Fighters|olice Association)))

which you could always feed to ack.

Changed to q{} per AnomalousMonk's post. Thanks AnomalousMonk!