Labour Union demanding Official Letter communication in English

In our organization we have PAN-India recruitment policy (Local Vs Pan India at 50% : 50%) as part of diversity and while recruiting candidates were tested for minimum English Proficiency. After recruitment workman are given extensive training in English and able to easily UNDERSTAND & READ English as many of the job related communications like Check sheet, Standard Operating Procedures are all English.
Their fluency is such an extent they make Power Point Presentations, while interacting with Management. Currently in wage negotiation in progress and there is a considerable gap in demand and the offer from the Management.
Suddenly, Union is expecting the communication in the local language, whenever there is an official communication is from the management. Is it legally tenable ? Is there any case law to refuse communication other than English? In future, if one of union officer bearers, who hails from Manipur can ask communication in Manipuri or other less known/spoken language, is it practical ?
Your thoughts please.

Generally all communication done with workers should be done either in Local Language or Understood by Majority of the Workers so please hire good translator to do all such translation once communication done with local Language/ Majority comprehendible Language then in case of any Labour Dispute company will prevail regarding the Comprehension of the Letter Matter.

Hi,
1- It is legally correct even though the language or the communication is english or any other local language. Thus, you need not to worry about legal aspect over the language.
2- Ideally most of the companies put notices or any communication in english and in the local language as well. Even the law also is in the same favor of putting the communication in the local language as well. Eg: you need to put abstract in english and local language as well to get the maximum understanding level.

local language means which is spoken over the state, and sign boards plus bus routes are written in that language also apart from english , a very simple understanding
abstract in local language also on "notice board" will be on safer side for employer, as in case of any non-compliance, he has upper hand in putting notice in "legible and worth understanding language" also

Purpose of communication is to make people understand.So kindly write in English and local local language as well.
Ensure what is written in both languages is exactly same.

Some unions and leaders demand communication to be issued to them in the local language while they would be communicating all along in English. I had dealt a practical situation where the leader refused to accept a show cause notice issued to him in English and demanded its Hindi copy. He also demanded a copy of the documents in Hindi and he was politely replied quoting more than half a dozen letters issued by him to the management in English and termed his attempt as mischievous and for wasting time. He tried to raise the issue in Labour Court but could not succeed and the matter ended there.

Dear KK: Greetings ! You have referred a unsuccessful attempt by Union in labour court where Union tried to wriggle out but it was not entertained. Possible to get the judgement/order copy

Dear Mr.Shriram,
It seems that Mr k k had the judgement in his favour because of the facts. Since he had asked the management to give the copy in local language but earlier was primarily communicating in English. so naturally the Honorable Court is going to take this as frivolous or mischievous attempt.
My observations are based on his small comment but it might be a little bit different.
You should see the facts of your case and relevant applicable laws.