Airlines cannot allow passengers bound for the US to board without a visa, otherwise they are subject to penalties and fines by the US government. It must be remembered that having a visa does not guarantee admission to the US. It merely allows a person to apply for admission at a port-of-entry. The person is inspected by a US immigration officer upon arrival, and he or she may still be denied admission if the officer determines that the person is inadmissible.
There are 2 kinds of visas – immigrant and non-immigrant. An immigrant visa entitles the holder to apply for admission to the US for the purpose of living and working there on a permanent basis. A non-immigrant visa, on the other hand, is for a temporary visit limited to the purposes for which the visa was issued. Generally, a non-immigrant visa is not compatible with any immigrant intent. This why non-immigrant intent must be demonstrated in non-immigrant visa applications. If admitted, the non-immigrant is expected to return to his or her home country once the purposes have been served. For example, a non-immigrant admitted as a student is only supposed to study in the US. Any deviation from the terms of the visa under which a person is admitted into the US is a violation of law, i.e overstaying, working without authorization, etc. Some violations, if not already criminal offenses in themselves, can lead to such.
The law presumes that all applicants for admission are intending immigrants. An immigrant visa applicant will have to show entitlement to this visa by satisfying immigrant petition requirements like family relationship or a job offer. It must be noted that some petitions based on job offers require a certification from the US Labor department that no US workers are available for the particular job. In addition to the petition requirements, an applicant must show admissibility.
This presumption of immigrant intent is the major hurdle that non-immigrant visa applicants face. The applicant must first convince the US consular official that he or she is only going to the US temporarily and will return home to the Philippines after the visit. If a non-immigrant visa is issued, the applicant must then be prepared to convince the immigration officer inspecting him or her upon arrival in the US of the same if challenged.
There are other requirements when applying for a non-immigrant visa, depending on the type. Some categories require a previously approved petition. Some are subject to an annual quota. So decide first what your plans are to determine the specific requirements of the appropriate visa.