to be the most important person or thing competing for sb's time, money, etc. and to be dealt with or paid for before other people or things :
The children always have first call on her time.
to be the most important person or thing competing for sb's time, money, etc. and to be dealt with or paid for before other people or things :
The children always have first call on her time.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005