The Party's Deputy Office Secretary Mrinal Kanti Das said that Siddique has been also informed about the decision to drop him from the party's policy-making Presidium.
The showcause notice has been sent to Siddique's permanent address in Tangail's Kalihati Upazila by registered post from the capital's Jigatala post office on Tuesday, said the AL leader.
The letter, signed by AL General Secretary Syed Ashraful Islam, has been issued in line with the decision of the party's Central Working Committee on Sunday.
Now in Kolkata, Siddique said he will reply to the show-cause "as and when I get it and within the time limit mentioned".
The letter mentions his controversial remarks over Hajj in in New York. It reads:" Your statement is not only outrageous and unexpected, but it has also hurt the sentiments Muslims of Bangladesh. It contradicts with the Awami League's policy and is a clear violation of the party's ideology and articles of association."
It gave Siddique seven days to explain as to why he will not be expelled from the party for his comments on Hajj.