Attorneys said in a court filing late Tuesday that plans to replace waist-high barriers this month with taller fencing in a wildlife refuge, national monument and conservation area are being delayed until October.
Authorities plan on using Defense Department funds under President Donald Trump's emergency declaration.
The Center for Biological Diversity last week asked a federal judge to halt work on 68 miles (109 kilometers) of border wall, saying the government unlawfully waived dozens of laws. Environmentalists say the new barriers will damage wildlife habitat.
The government says the replacement fencing is crucial to national security.
It will proceed with construction on a two-mile stretch near an official border crossing beginning next week.
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