‘For this reason at that time certain Chaldeans came near and brought accusations (literally ‘ate their pieces' i.e. chewed over publicly what they had heard) against the Judeans.'
We are probably to see these Chaldeans as belonging to the ‘wise men', who were possibly secretly nursing a grudge against these young upstarts. This gave them their opportunity. They had been shamed by Daniel, and they had quickly forgotten that he had saved their lives. And these youngsters had been given positions far above their station because they were his protégés. It is also quite probable that they did not like the way Daniel was carrying out his duties as chief of the wise men. But they had to be careful with him, while these youngsters were vulnerable and had played into their hands.
Alternately they may have been ethnic Chaldeans who lived in southern Babylonia, who were proud of being ‘true native Babylonians' and resented foreign upstarts. Note the reference to ‘the Judeans'. Either way there was clearly resentfulness here.