The union, a professional public organization, said in a statement that it "unites architects and urban planners of various political views whose professional activity should be free of any political component."
"No one in the union's leadership has agreed to join the people's front, to say nothing about the rest of the organization," union spokeswoman Natalya Palkina said in comments carried by Gazeta.ru.
She said the front had sent an invitation to join, and the union's leadership had decided to reject it at a meeting Monday.
As of late Monday afternoon, the union was still listed on the front's web site.
Under Putin's initiative, the front was created in early May to consolidate public groups around United Russia and mobilize the public around the Putin-led party ahead of State Duma elections in December. Members of the front have been offered United Russia seats in the Duma.
Hundreds of public groups and associations have been swept into the front, with some of their members learning about it after the fact and then sharing their surprise on their Internet blogs.
Among them was Union of Architects member Yevgeny Ass, who published an open letter on June 23 that said he had found the union listed on the front's web site and that he would quit the union if it remained a part of the front.
More than 100 union members joined Ass in his protest.
Maria Lipman, a political analyst with the Carnegie Moscow Center, said the architects' demarche would not have a big effect on the front's prestige and would not result in any punishment for the union.
"This only has meaning for those who are interested in politics, and everyone else doesn't care," she said, adding that the front invokes in many Russians the traditional Soviet-era response to follow the wishes of the country's leadership without making a fuss.
Alexei Mukhin, a political analyst with the Center for Political Information, said the architects' ire was no surprise because they are less dependent on the state than the members of other unions of arts professionals.