Whether someone is getting "equal pay for equal work" is really going to depend on how a person defines “equal work” - but it could also depend on how you define “equal pay”.
I’ll start with the “equal work” concept.
Say you own a fast food franchise and hire a group of entry level employees. They all have the same level of required education (can read the employee manual) and experience (none), and start the same day. This avoids such factors as differences in job related education, work experience, and seniority in the organization.
Two of them, Alex and Bailey, are even working the same shifts, side by side.
At the end of the first month, you look at their stats.
Alex averages 33 orders an hour.
Bailey averages 45 orders an hour.
Corey averages 18 orders an hour.
Dell averages 36 orders per hour.
Ed averages 48 orders an hour.
Should Bailey be getting paid more than the others, because Bailey is getting more work done?
Should Alex and Dell make similar amounts, because they get similar amounts of work done?
Should Corey make less than the others, because Corey is less productive?
Now, let’s look at other factors.
Alex and Bailey work the same schedule (M-F, days), side by side.
Corey works the graveyard shift (Thu-M), when most employees would rather be asleep, and there are just fewer customers at that time.
Dell also works some graveyard shifts (Tu-W), but is also working weekend days (Sa-Su, 12 hour shifts), when most employees would rather be off.
Ed works the busiest shifts (F-Su, 11am through midnight) and works three 13 hour shifts.
There are fewer customers during the graveyard shifts, and 18 orders an hour is the average for all of your graveyard shift workers, who are alone at the register.
How much “other duties as assigned” work does each of the employee do?
What if Bailey is not able to bend and lift as much as Alex, so Alex unpacks the delivery truck, and also does the sweeping, mopping, bathroom cleaning, and emptying the trash cans? This takes Alex away from the register, and reduces Alex’s ability to earn good sales numbers.
As you can see, at first glance, all of these employees have the same job, and should arguably make equal pay. But on closer examination, we see that their jobs have different hours, working conditions, responsibilities, and opportunities.
Should they all get the same hourly pay?
Should there be a shift differential in pay for those working the less popular shifts (graveyard, weekends, and Friday evenings)?
How about a pay differential if the employee is doing more than their ‘fair” share of extra duties?
What about a performance/incentive pay raise?
Now let’s look at “equal pay”. Should that just be pay, or should it include benefits and other compensation that you, as an employer, will provide?
What if you find that due to maternity leave laws and other factors, you give female employees twice as many paid medical leave days - on average - as you give male employees?
What if you have to pay twice as much to provide medical insurance benefits to employees who have a spouse or child/ren?
To sum things up, there are a lot of factors that go into measuring work and pay, so it is not very easy to fairly claim equal work or even equal pay without considering those factors.