What is rules to get Per DM for H1bs?
Please suggest.
Answer:
It's per diem, not per DM, and it is latin for "per day". Rules are no different for H1B than for US workers. The rules are tax-related and i believe are made by the Internal Revenue Service. Basically you get an allowance for maintaining a second home if your commute would be too far from your primary home. If it is commutable (generally 50-60 miles) you don't get per diem. For H1 workers, a helpful (but not conclusive) test is whether or not the employer gave you a separate LCA that covers the remote city (unless your primary LCA covered both cities). If no separate coverage on an LCA, it shows they are treating the worksite as commutable, which would weigh against per diem eligibility.
Note that you can get per diem only for a year, or until you know that your project will extend beyond a year, whichever comes first. For example, if you go on project with a 9 month initial duration, and in month 8 the client extends it for another 6 months, you lose the per diem as soon as the extension is ANNOUNCED; you don't get the rest of the year because you now (at month 8) have reason to know you will be there MORE than a year.
PS--I don't think the per diem counts toward your wages or salary for purposes of determining whether the employer is paying you the higher of the prevailing wage or actual wage paid to similarly situated US workers.