For decades American hiring routinely asked applicants what they currently earn. A number of states and cities restricted the question, and the reasoning is mechanical.
The question anchors the offer
When an employer knows a candidate's current pay, the offer is usually constructed as an increment above it rather than from the value of the role.
That converts every past salary decision into an input for the next one. A single low starting salary propagates through each subsequent move for the length of a career.
Because women and workers from lower-paying regions and sectors start lower on average, the practice transmits an existing gap forward regardless of any bias at the hiring employer.
The restrictions differ substantially
Some jurisdictions bar asking entirely, some bar relying on the information if volunteered, and some require an employer to disclose a range on request or in the posting.
Coverage also varies by employer size and by whether the role is public sector, and the rules change over time as legislatures revise them.
An applicant unsure what applies where she lives or where the job is located should check her state labor department, and an employment attorney is the right source for a specific dispute.
Pay range transparency is the companion measure
Restricting the question removes information from the employer. Posting a range supplies information to the candidate, and the two together change the negotiation more than either alone.
Where ranges are posted, candidates negotiate against a published band rather than against a guess, which reduces the advantage held by applicants with better informal networks.
What replaces the question in practice
Employers still ask about salary expectations, which is not the same question and is generally permitted. The applicant supplies a number, which anchors in the other direction.
Preparing that number from role-based information rather than from current pay is the practical response, and public salary data for the occupation and metropolitan area is the usual basis.
Enforcement is complaint-driven
These laws are typically enforced when someone reports a violation rather than through routine inspection, so their effect depends on applicants knowing the rule exists.
Awareness is uneven, and applicants who most need the protection are frequently the least likely to have heard of it, which limits the measured effect of an otherwise sound mechanism.
That gap between a right and its use is common across employment law, and it is why disclosure requirements in postings tend to outperform prohibitions the candidate must invoke.