The ruling Congress also hit out Modi, asking, "Is this Cooperative Federalism which PM talks about?"
An "upset" state Government said this had sent a "bad message" and virtually blamed the Prime Minister's Office(PMO) for Siddaramaiah not being extended an invitation to the NASSCOM event here yesterday.
"Not inviting the Chief Minister for the programme (NASSCOM event) - it has sent a bad message. We are all upset with that," State Law and Parliamentary Affairs Minister T B Jayachandra told reporters on the sidelines of the Cabinet meeting here.
According to the Chief Minister's office, Siddaramaiah did not get an official invitation either from NASSCOM or Prime Minister's Office.
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Questioning Modi's often-repeated statements about strengthening federal structure, Jayachandra said, "He always speaks of strengthening the federal structure and sundry other things, but ultimately what is he doing? Is he taking all the parties together?"
According to the protocol, the participation of Chief Minister is necessary and it is in the "norms" that the PMO invites him for any official event, Jayachandra said.
Asked whether the state government would write a letter to the Prime Minister on the issue, he said the ministers had impressed upon the Chief Minister to convey it to the PMO.
"We have impressed upon the Chief Minister also that it should be made known to the PMO, and let us see what action the Chief Minister takes," he said.
NASSCOM has not reacted to the issue yet.
"CM Karnataka not invited in NASSCOM function attended by PM and German Chancellor in Bangalore. Is this Cooperative Federalism which PM talks about? Would CM Gujarat also have not been invited if this function was in Gujarat?" party General Secretary Digvijaya Singh tweeted.
Along with the German Chancellor, Modi had taken part at the meet, 'Indo-German Summit 2015: Digitizing Tomorrow Together'.
The Prime Minister also hosted a special lunch for Merkel with leading Indian CEOs at the summit which was attended by several industry biggies, including Wipro Chairman Azim Premji, Chairman of the Aditya Birla Group Kumar Mangalam Birla, Tata Consultancy Services CEO N Chandrasekaran, ICICI Bank CEO Chanda Kochhar and L&T Chief A M Naik.
Siddaramaiah had received and seen off the Prime Minister at the HAL airport here and exchanged greetings and pleasantries.