'has been obligatory' is a valid and perfectly correct phrase in written English.
You can use it when you want to express that something has been required or mandated for a period of time, usually in the past. For example: "The wearing of protective clothing has been obligatory in this factory for the past five years."
It has been obligatory since Wittgenstein to feel bad about language.
Since the coalition government came to power in 2010, immunity to reason has been obligatory among Trident apologists.
A good thing, then, that since 1988 teaching about the Holocaust has been obligatory at Austrian schools, and that all schoolchildren must visit the former concentration camp at Mauthausen.
To do so, it has been obligatory for the firms to consider production side activities while customer requirements are on the other side of competition.
Stunning has been obligatory in the European Union since 1979 in order to spare animals "avoidable pain or suffering", though most member states make exceptions for religious communities.
Still, women applying to the National Police force have been given virginity, or "two-finger" tests since at least 1965 a few months ago, the Indonesian coordinating minister for politics, law, and security told the press that giving female military recruits a hymen check has been obligatory for a while now.
It was not that long ago that including at least one or two county chairmen would have been obligatory on any list of the 10 most powerful New Yorkers: Carmine DeSapio, Vincent F. Albano, Meade Esposito, Stanley M. Friedman, Donald R. Manes and Thomas J. Manton, to name a few.
Utzon always dressed with subtle taste — "It was clear he had a very good tailor in Copenhagen" — but the younger architects were free to abandon the suit and tie that would have been obligatory in most Sydney architecture firms of the day.
It could also substitute for forms of travel that previously would have been obligatory, such as for job hunting.
But while McConaughey's praise may have been obligatory, the Emmy nominees are an especially well-credentialed bunch this year.
Independent of compulsory admission, court decision rates with regard to physical restriction, which have been obligatory since 1992, increased markedly from 12 to 90.
