It would appear that the Trump administration is being sued for blocking critics on twitter

They argue that since the trump account is being used for official statements and public discussion, that blocking these people is a violation of their first amendment rights.

You can read the actual complaint here:
2017-07-11-Knight-Institute-Trump-Twitter.pdf

It's a complaint for "DECLARATORY AND INJUNCTIVE RELIEF" which means they want to court to say who is right (declaratory) and make trump unblock them (injunctive), i think.