を禁じ得ない goes after a noun for a feeling and means you cannot hold it back: "I cannot help feeling", "I cannot keep back my tears". is "suppress" and is "cannot", read えない. It is written, formal language – editorials, speeches, formal commentary – and the feeling is the speaker's own.
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Hearing the stories of the disaster victims, I cannot help but feel sympathy.
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I cannot suppress my anger at his irresponsible attitude.
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Listening to her speech, I could not hold back my tears.
The noun is a feeling or a reaction: , , , , , , . A verb cannot go in front: ×泣くを禁じ得ない. What caused the feeling usually takes .
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I cannot suppress my indignation at the government's slow response.
を禁じ得ない or ずにはいられない
means the same, "can't help doing", but takes a verb, and it is the one you can use in speech. In conversation you would just as often say what happened:
,
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Watching the final scene of that movie, I could not hold back my tears.
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Watching the final scene of that movie, I couldn't help crying.