work suspension, is is valid or not?

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My wife are working as production operator in a Japanese company here in the Philippines, one day the management conduct an audit and she was audited. The finding for her is that she did not insert her uniform (jack shirt) inside her rubber glooves where in this is one of the procedure inside the production because their skin must not be exposed. She explain her side, she did not inserted her uniform because the glooves issued to them was small and they canno't insert the uniform anymore, besides her skin was not exposed. After a few weeks her line leader tell her that she was suspended for three days because of her violation. My question is, is it valid that she was issued suspension without giving first a written warning? It was just her first violation.