The three, all student union officers at Kingsway College who were questioned by police after the paint attack, have been barred by a High Court order from entering college premises until a disciplinary hearing on January 18.
They face a list of charges, including disrupting "academic and administrative life" by organising an occupation of college buildings after the paint attack, and "bringing the college into disrepute".
Managers at Kingsway have made the accusations according to a pre-incorporation disciplinary code drawn up under the old Inner London Education Authority (ILEA) for use by all colleges in the city.
Kingsway is in the process of producing a new code of its own, but the document has yet to be ratified by college governors, and lawyers have advised using the older version instead.
However, the suspended students, who include student union president Nick De Marco, claim the college has not used the ILEA procedure since incorporation and has relied instead on a relatively informal arrangement used with the union's co-operation.
Mr De Marco, 28, said: "The union has not ratified this ILEA procedure, and was not aware it existed. If they pull a new code out of the bag which we have never seen it does not seem very fair."
He and fellow A-level students Karen Doyle and Naveed Malik would not have been suspended under the usual, "informal" procedures, he claimed. The three are taking legal advice over challenging the use of the ILEA code, which college managers insist has been used at Kingsway before.
The students were arrested and questioned by police after paint and flour were thrown over Mr Mawhinney last November by demonstrators protesting at the Government's new Asylum and Immigration Bill. They were released on police bail.
The college disciplinary action relates to incidents on Kingsway premises after the paint attack. Managers say the students held an unauthorised press conference the following day, though the three claim they were simply attempting to ease intrusive media attention.
The accusations also centre on a conference on the Asylum Bill, organised by students, which ended in an occupation of a college room.
Mr De Marco said he and his two fellow students would not break the ban on entering Kingsway, but would demonstrate outside the buildings to highlight their case. The college's real intention was to expel them, he claimed.
Kingsway students say they are anxious to draw attention to the Asylum Bill because they say a third of them could lose their benefits under the new legislation.