Is agreement with employer legal?

[abhaya_kumar]

I am currently working with companyA and CompanyA is holding my H1B. Just few days back I got good offer form CompanyB and interested in joining companyB. But now problem is I have a agreement(signed by both parties) with CompanyA which says if I will break agreement within a year then I would have to pay $10,000 to them, since they have spend some money in bringing from abroad. But I am breaking this agreement Just after 3 months.

Now, my question is whether this agreement and paying that much amount is legal or not?

waiting for reply

Thanks & Regards
Abhaya