WASHINGTON — In his latest confrontation with Congress, President Obama on Tuesday blocked Republican efforts to overturn new union-friendly federal regulations issued by his administration.

Mr. Obama rejected a resolution passed by both houses of Congress that would have reversed rules to speed up and streamline union elections, the equivalent of a veto. Republicans referred to it as the “ambush election” rule and argued that it would be unfair to businesses.

The showdown over the labor rules represented a new front in the larger battle between Mr. Obama and the Republican-controlled Congress over the scope of his executive power. With the two sides at loggerheads over most legislation, they have been fighting instead over how far Mr. Obama can and should go in using his authority as president to advance his agenda.

The union regulations, issued in December and scheduled to take effect on April 14, reflect the kind of policy changes Mr. Obama’s team can enact through the various agencies of the executive branch. The president has also relied on his own power to make it possible for millions of illegal immigrants to stay in the country, to modify details of his signature health care program and to advance limits on power plant emissions blamed for climate change.