pre-employment bonds

my sister is currently employed and has submitted resignation already. she has already signed a pre-employment contract to the other company she wishes to work for.

the case is, company #1 offers her a pay equivalent to that of company #2 offers her. now, my sister thinks of not leaving company #1 but worries about her signed pre-employment contract with company #2.

in the pre-employment contract, it says that there will be a fine of P50,000 if she opts not to continue employment with company #2.

my question is: is there such a law that would deny or support the said pre-employment contract?

hoping to receive comments and lawful advise from you. thanks much for the help.

the law on contracts. this matter of bonds has not been decided upon by the supreme court. it is risky to ignore them, but if you did, the company has to file a case to collect.