At least eight other churches have been firebombed or vandalised since the court ruling allowing the Malaysian Catholic weekly newspaper, the Herald, to use the word "Allah" to refer to God in its Malay-language edition.
The legal firm attacked on Thursday represents the Herald.
Speaking to The Associated Press news agency, S Selvarajah, one of the firm's lawyers, said staff had arrived at work to find several locks and steel grille doors cut, drawers ransacked and papers strewn on the floor.
"Criticism and dissent are legitimate forms of expression, but threats, coercion, intimidation or violence are unacceptable"
Ragunath Kesavan, Malaysian Bar president
Selvarajah said a laptop was missing while a mobile phone service provider's shop and tuition centre on the first floor were not broken into.
"Only our office has been targeted," he said.
"It looks like it is an intimidation tactic … We anticipated something will happen. We are definitely upset about this."
Father Lawrence Andrew, the editor of the Herald, said he was "very concerned" about the break-in which he believes is linked to the ongoing court case.
"The law firm does not have any money or many valuables so we believe this is purely aimed at intimidation," he told AFP.
Meanwhile, the Malaysian Bar Association condemned the attack and urged a "thorough investigation".
Ragunath Kesavan, the president, said in a statement that lawyers must be free to represent their clients "without fear or favour".
"Criticism and dissent are legitimate forms of expression, but threats, coercion, intimidation or violence are unacceptable," he said.
'Acts of extremism'
Najib Abdul Razak, the Malaysian prime minister, has condemned the attacks that have followed the ruling last Friday.
He has vowed to do everything to bring the culprits to justice, and denied accusations that Umno, the party he leads, was racist.
Earlier this week the Malaysian home ministry in a briefing for foreign diplomats condemned the "acts of extremism" and pledged to "protect the sanctity" of the country's diverse religions.
The Herald has been using Allah in its Bahasa Malaysia, the country's national language, publication since 1995, but it was not until 2006 that it was warned by the government to stop using "Allah" to refer to God.