https://www.uscis.gov/policy-manual/volume-7-part-e-chapter-...
most of us here have been hiring managers in the bay area so we have been exposed to this. My exposure was you are fairly locked into one company. I had friends who had to go home abruptly when fired. We would have to buy their cars so we could sell them slower at non-fire sale prices for them. But this was late 90s through early 2000s. Maybe it's different.
Changing or Leaving Your H-1B Employer
Q. What is “porting”?
A. There are two kinds of job portability, or “porting,” available based on two different kinds of employer petitions:
H-1B petition portability: Eligible H-1B nonimmigrants may begin working for a new employer as soon as the employer properly files a new H-1B petition (Form I-129) requesting to amend or extend H-1B status with USCIS, without waiting for the petition to be approved. More information about H-1B portability can be found on our H-1B Specialty Occupations page.
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Q. How do I leave my current employer to start working for a new employer while remaining in H-1B status?
A. Under H-1B portability provisions, you may begin working for a new employer as soon as they properly file a non-frivolous H-1B petition on your behalf, or as of the requested start date on the petition, whichever is later. You are not required to wait for the new employer’s H-1B petition to be approved before beginning to work for the new employer, assuming certain conditions are met. For more details about H-1B portability, see our H-1B Specialty Occupations page, under “Changing Employers or Employment Terms with the Same Employer (Portability).”
https://www.uscis.gov/working-in-the-united-states/h-1b-spec...
When can I begin working for a new H-1B employer if I change employers?
If you are changing H-1B employers, you may begin working for the new employer as soon as they properly file a non-frivolous Form I-129 petition on your behalf, or as of the requested start date on that petition, whichever is later.
To be eligible for portability, you must not have been employed without authorization from the time of your last admission into the United States, and your new employer must properly file a new, non-frivolous petition before your H-1B period of authorized stay expires.Though there's pretty hard limitations on what you can transfer with - it has to be the same sector, similar limitations on minimum salary, and requires work on the new employer's part to move the H1B to them (so you can't keep it quiet, and it's another barrier as it's non-zero cost for lawyers etc. to actually do that).
You're not locked into one employer on an H1B. Once you are here it is possible to switch jobs relatively easily since you do not need to go through the lottery again.
> as far as I know employment law leaves them quite free to offer a lower salary
"The H-1B employer must pay its H-1B worker(s) at least the “required” wage which is the higher of the prevailing wage or the employer’s actual wage (in-house wage) for similarly employed workers."
https://www.dol.gov/agencies/whd/fact-sheets/62g-h1b-require...
But yes, as far as I know companies would usually offer an H1B applicant lower salary. They know the candidate will need visa sponsorship because the candidate has to say up front (usually in the first conversation) if they are authorized to work in the US. If the companies know they will have to undertake costly sponsorship, and as far as I know employment law leaves them quite free to offer a lower salary: foreign nationals are not a protected class so salary discrimination on the basis of who will need visa sponsorship is just to be expected in the current system...