The phrase "already called upon" is correct and usable in written English.
It can be used to indicate that someone or something has been requested or summoned previously.
Example: "The committee has already called upon experts to provide their insights on the matter."
Alternatives: "previously summoned" or "already requested".
They noted that their country's soldiers were already called upon to supervise security forces in Afghanistan, and that American planes had run hundreds of missions into Afghanistan from the Turkish air base in Incirlik.
The Italian government has already called upon the private sector to help restore other ancient monuments, including the Colosseum in Rome and the Trevi fountain.
But the Three Leagues had already called upon the Swiss for help and troops from Uri had already arrived in Chur.
Furthermore, the effects of financial fragmentation have doubled the burden of families and businesses, which, we should not forget, were already called upon to make great sacrifices.
The recruits have added depth to a side that could already call upon Dusan Kuciak, voted the Ekstraklasa's best goalkeeper last season, and Serbian winger Miroslav Radovic, who was the player of the year.
There is a move gaining some momentum, with more than a million signatures already, calling upon the Electoral College to choose the person who won the most votes as the next president.
Moreover, researchers in these systems can already call upon a wealth of existing data (Callaghan et al., 2004) from detailed population and ecosystem monitoring, including long time series of the dynamics of populations and communities.
Waiting to be called upon again.
Japanese and South Korean officials have already publicly called upon the United States to take steps to ensure that no StarLink corn reaches their shores.
As has already been called upon by different organisms, and more specifically by the FDA, it seems necessary to conduct experimental studies similar to those used in pharmacological treatments, in order to obtain sufficient scientific evidence of the possible usefulness of these tools.
