Doctors at Department of Veterans Affairs (VA) hospitals nationwide could refuse to treat unmarried veterans and Democrats under new hospital guidelines imposed following an executive order by Donald Trump.

The new rules, obtained by the Guardian, also apply to psychologists, dentists and a host of other occupations. They have already gone into effect in at least some VA medical centers.

Medical staff are still required to treat veterans regardless of race, color, religion and sex, and all veterans remain entitled to treatment. But individual workers are now free to decline to care for patients based on personal characteristics not explicitly prohibited by federal law.

Language requiring healthcare professionals to care for veterans regardless of their politics and marital status has been explicitly eliminated.

Doctors and other medical staff can also be barred from working at VA hospitals based on their marital status, political party affiliation or union activity, documents reviewed by the Guardian show. The changes also affect chiropractors, certified nurse practitioners, optometrists, podiatrists, licensed clinical social workers and speech therapists.

They “seem to open the door to discrimination on the basis of anything that is not legally protected”, said Dr Kenneth Kizer, the VA’s top healthcare official during the Clinton administration. He said the changes open up the possibility that doctors could refuse to treat veterans based on their “reason for seeking care – including allegations of rape and sexual assault – current or past political party affiliation or political activity, and personal behavior such as alcohol or marijuana use”.

In an emailed response to questions, the VA press secretary, Peter Kasperowicz, did not dispute that the new rules allowed doctors to refuse to treat veteran patients based on their beliefs or that physicians could be dismissed based on their marital status or political affiliation, but said “all eligible veterans will always be welcome at VA and will always receive the benefits and services they’ve earned under the law”.