AP Syllabus focus: ‘Hiring another worker can require a wage increase for all existing workers, which raises marginal factor cost.’
In monopsonistic labour markets, a single major buyer of labour faces an upward-sloping labour supply. That creates a key complication: hiring one more worker can force a higher wage for current workers, raising the firm’s true marginal cost of labour.
Why adding one worker can raise wages for everyone
A monopsonist is a dominant employer in a labour market that must offer a higher wage to attract additional workers because the labour supply to the firm is upward sloping.
The “same wage for similar work” constraint
In most textbook monopsony models, the firm cannot pay different wages to identical workers performing the same job at the same time. As a result:
To hire the next worker, the firm must post a higher wage.
That higher posted wage applies to:
the new hire, and
all existing workers in that job category.
This is exactly the syllabus idea: hiring another worker can require a wage increase for all existing workers, and therefore the incremental cost of hiring is more than just the wage of the additional worker.
Key terms you must connect: wage, total labour cost, and marginal factor cost
The wage is the price of labour, but in monopsony it is not the same as the marginal cost of labour to the firm.
Marginal factor cost (MFC): The additional cost to the firm of hiring one more unit of an input (here, labour), including any required wage increases paid to existing workers.
The wage increase for existing workers matters because it changes the firm’s total labour cost when employment rises.
The total labour cost mechanism
When the firm raises the wage to attract an additional worker:
Per-worker pay increases.
The increase applies to every worker already employed.
Therefore, total labour cost rises by more than the new wage alone.
Even if the wage only rises slightly, multiplying that small increase by many existing workers can create a large extra cost.
How wage increases translate into a higher MFC
A useful way to formalise this is to distinguish:
the wage rate the firm must offer to employ a given number of workers, and
the marginal factor cost, which captures the full incremental cost of expanding employment by one worker.
= marginal factor cost of labour (dollars per worker)
= change in total labour cost (dollars)
= change in labour employed (workers)
Between the wage and MFC, the central logic is:
TLC increases for two reasons when hiring expands:
paying the wage to the additional worker, and
paying a higher wage to all inframarginal (previously hired) workers.
Therefore, MFC exceeds the wage at that employment level whenever expanding employment requires a higher wage.
Visual/graph intuition (without calculation)
When you graph the labour market from the firm’s perspective:
This figure combines the market labor supply , labor demand (MRP), and the monopsonist’s marginal expenditure curve (ME, equivalent to MFC). It visually shows the monopsonist choosing employment where and then paying the wage read off the supply curve at that employment level, yielding lower employment and a lower wage than the competitive outcome. Source
The labour supply curve to the monopsonist shows the wage required to employ each quantity of labour.
The MFC curve lies above the labour supply curve because:
This diagram shows the firm’s upward-sloping labor supply curve and the marginal cost of labor curve (i.e., MFC) lying above it. The vertical gap illustrates the wage spillover: hiring an additional worker requires paying a higher wage not only to the marginal hire but also to previously hired (inframarginal) workers. Source
to employ one more worker, the firm must move up the supply curve (a higher wage), and
that higher wage is paid across the existing workforce.
Interpreting “existing workers” and “inframarginal” workers
The existing workers are inframarginal workers—those already employed before the firm decides to hire an additional worker. Their wages may have to rise even though their employment status does not change, creating an extra cost that is part of MFC.
What to emphasise for AP exam explanations
When a prompt asks why hiring another worker raises marginal factor cost in monopsony, focus on the wage spillover onto current workers:
Upward-sloping labour supply: more labour requires a higher wage offer.
Uniform wage assumption: the higher wage applies to all comparable employees.
Wage spillover: raising the wage for existing workers increases total labour cost sharply.
Result: the marginal cost of hiring (MFC) is greater than the wage of the additional worker.
Common confusion to avoid
Do not say MFC is higher because the firm “wants more profit” or because workers become less productive.
The wage increase for existing workers is a pricing (cost) effect, not a productivity effect.
The key cause is the firm’s need to raise the wage to expand employment, combined with paying that wage broadly across workers.
FAQ
Sometimes, yes, if the firm can practise wage discrimination (e.g., different contracts, job titles, or hiring cohorts).
However, it may be limited by:
equal pay rules and collective agreements
morale/retention concerns
information problems (workers discovering pay differences)
If discrimination is feasible, the “raise wages for everyone” effect is weaker, and MFC can move closer to the wage for the marginal hire.
Multi-period contracts can “lock in” wages for current workers, so the firm may only need to offer a higher wage to new hires.
Even then, costs can rise through:
renegotiation pressure as contracts expire
internal pay scales that trigger automatic adjustments
retention costs if existing workers threaten to quit
So contracts can delay, but not always eliminate, the spillover to existing wages.
A one-off bonus targeted at new hires can reduce the need to raise the posted wage for everyone, limiting spillover to existing workers.
But the firm should consider:
whether bonuses become expected for all future hires
whether existing workers demand similar bonuses
whether bonuses are cheaper than a permanent wage increase over time
The key is whether the bonus truly stays marginal rather than spreading to inframarginal workers.
When employment is high, a small wage increase applied to all existing workers is multiplied across a large workforce.
Intuitively:
raising the wage by $ \Delta w $ for $L$ existing workers adds about $L \cdot \Delta w$ to payroll
that extra payroll is part of the marginal cost of expanding employment
So the same required wage increase can create a bigger MFC gap at larger employment levels.
High turnover can weaken the “existing worker” channel because fewer workers remain on the old wage when the firm adjusts pay.
But turnover can also strengthen wage pressure if:
the firm must raise wages to retain staff while recruiting
quitting increases the wage needed to attract replacements
Whether spillover rises or falls depends on how hiring, retention, and wage posting interact in that specific labour market.
Practice Questions
(2 marks) Explain why, in a monopsonistic labour market, hiring one additional worker can increase the firm’s wage payments to existing workers.
1 mark: States that to attract the next worker the firm must offer a higher wage because labour supply is upward sloping.
1 mark: Explains that the higher wage must be paid to existing (inframarginal) workers as well, increasing total wage payments.
(5 marks) A firm is the sole major employer of a type of labour in a local area. Using economic reasoning, explain how a wage increase required to hire an extra worker affects the firm’s marginal factor cost of labour, and why this marginal factor cost can be greater than the wage.
1 mark: Identifies that the firm faces an upward-sloping labour supply and must raise the wage to increase employment.
1 mark: States that the higher wage applies to more than just the marginal worker (i.e., also to existing/inframarginal workers).
1 mark: Explains that total labour cost rises by the wage for the new worker plus the wage increase paid across current workers.
1 mark: Links this to as the relevant marginal cost concept.
1 mark: Concludes that MFC exceeds the wage because the incremental cost includes the higher wage paid to existing workers.
