Whose votes...

"But the head of the DUP, whose votes the government of British Prime Minister Theresa May is dependent on to pass legislation, repeated her rejection of the suggestion on Monday, saying she would not create barriers to business with the rest of the United Kingdom to allow smooth trade with Ireland." (Reuters.)

Is whose votes the government of British Prime Minister Theresa May is dependent on to pass legislation a non-restrictive relative clause in the sentence above?