READ: Mnuchin refuses to provide Trump's tax returns

Treasury Secretary Steven MnuchinSteven Terner MnuchinCharitable giving by individuals down in first year under Trump's tax law: study Charitable giving by individuals down in first year under Trump's tax law: study Congressional leaders, White House officials to meet Wednesday on spending MORE on Friday told Congress that the department will not provide President TrumpDonald John TrumpGOP senator introduces bill to hold online platforms liable for political bias Rubio responds to journalist who called it 'strange' to see him at Trump rally Rubio responds to journalist who called it 'strange' to see him at Trump rally MORE's tax returns.

The request "lacks a legitimate legislative purpose," Mnuchin told House Ways and Means Committee Chairman Richard NealRichard Edmund NealHouse Dems release bills to renew tax breaks, expand tax credits for workers and families House Dems release bills to renew tax breaks, expand tax credits for workers and families Trump: My 'financial statement' will probably come out 'at some point' MORE (D-Mass.) in a letter.

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Refusing to provide the information, which House Democrats subpoenaed, will likely trigger Democrats to pursue further legal action.

The standoff is the latest escalation in House Democrats' attempts to obtain documents from the Trump administration.

Read Mnuchin's letter below: