Monopsony vs Labor Union
Monopsony and Labor Union are related concepts in AP Economics that students often mix up. A monopsony is a market structure with a single buyer and many sellers, giving the buyer market power. A labor union is an organized group of workers that bargains collectively with employers over wages, benefits, and conditions. Here is how they compare side by side.
In a monopsony, the single buyer can influence the price of the product by changing the quantity it purchases. This allows the monopsonist to pay a lower price than in a competitive market. Monopsony power can arise in factor markets, such as a large employer in a small town.
By negotiating as a group, unions gain bargaining power individual workers lack and can raise wages above the competitive level. This can reduce employment in unionized firms and is a form of market power in labor markets.
Monopsony vs Labor Union: Wage-Setting Power on Opposite Sides of the Market
| Monopsony | Labor Union | |
|---|---|---|
| Which side holds the power | The buyer of labor, a single dominant employer | The sellers of labor, acting as one organised group |
| What it controls directly | How many workers to hire, knowing that hiring more lifts the wage for everyone | The wage and conditions it will accept, backed by the threat of a strike |
| Effect on pay against a competitive market | Holds it below the competitive wage | Pushes it above the competitive wage |
| Pay against marginal revenue product | The wage sits below marginal revenue product, and the gap grows with the employer's power | Bargaining aims to close that gap or push pay past it |
| The extra curve on the diagram | Marginal resource cost, drawn above the upward-sloping labor supply curve | None, because the bargained rate flattens the supply curve at that wage |
| Effect of a binding wage floor on jobs | Employment can rise, all the way up to the competitive wage | A bargained wage above the competitive level reduces the number hired |
| Legal treatment | Restrained by rules against wage-fixing and no-poach agreements between employers | Protected by labor law guaranteeing the right to organise and bargain |
A single buyer hires fewer workers and pays each of them less than they bring in
Work through an illustrative hiring table. The town's labor supply is w = 4 + 2L, where L is workers and w is the hourly wage, and the employer's marginal revenue product is MRP = 40 - 2L. Hiring 5 workers means paying 14 dollars each, a wage bill of 70. Hiring 6 means paying 16 each, a bill of 96, so the sixth worker costs 26 dollars an hour rather than 16, because everyone already there gets a raise. That 26 is marginal resource cost. The sixth worker brings in 40 minus 12, or 28 dollars, so the firm hires. Try a seventh: the bill goes from 96 to 126, a marginal resource cost of 30, while the seventh worker brings in 40 minus 14, or 26. The firm stops at 6 workers paid 16 dollars an hour, each producing 28 dollars an hour of revenue. A competitive market would set the wage where supply meets marginal revenue product, at 4 + 2L = 40 - 2L, so L = 9 and w = 22. One buyer costs this town 3 jobs and 6 dollars an hour. The same step-by-step cost calculation is drilled at /calculate/marginal-factor-cost.
A union facing a single employer is bargaining over a gap that already exists
Keep the illustrative numbers above. The monopsonist pays 16 dollars while the competitive outcome is 22, so there are 6 dollars an hour of surplus sitting with the employer. A union that bargains the wage up to 22 does not simply take money from the firm; it removes the reason to restrict hiring, because once the wage is fixed by contract, taking on one more worker no longer lifts pay for everyone else. Employment can rise to 9. Push the bargained wage past 22 and the ordinary result returns, with the firm hiring fewer workers than 9 and a queue forming for the jobs that remain. This is why the effect of union power on employment is not one answer but two, and why the exam expects you to say which market you are in before predicting the direction. Where employers compete freely for workers, a union wage above the market rate reduces the number hired and shifts income toward those who keep their jobs. Where one employer dominates, the same bargaining can lift pay and jobs together. The underlying hiring rule is set out at /micro/factor-markets.
Frequently asked questions
Can a union raise wages without reducing employment?
Yes, when it bargains with an employer that has monopsony power, because that employer already hires fewer workers at a lower wage than competition would produce. Raising the bargained wage toward the competitive level can lift pay and hiring at the same time, and only a wage pushed beyond that level starts cutting jobs.
Why does a monopsony pay less than marginal revenue product?
Because attracting one more worker forces the employer to raise the wage for everyone already on the payroll, so the true cost of that worker is higher than the wage on the offer letter. The firm hires until that cost equals marginal revenue product, which leaves the posted wage below what the last worker brings in.
What is a bilateral monopoly in the labor market?
It is a market with one buyer of labor facing one organised seller, typically a dominant employer and a union representing all of its workers. Theory pins the outcome only to a range, with the low end near what the employer would pay unopposed and the high end near what the union could extract, and relative bargaining strength decides where inside that range the wage lands.
Live Factor Markets graph. Drag the curves, or open the full version.
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