The White House is moving ahead with plans to impose tariffs against Mexico in response to a surge in illegal migration, but President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE could decide over the weekend to delay them, a senior administration official said Friday.

Marc Short, chief of staff to Vice President Pence, said a “legal notification” will be posted on Friday that Trump will slap a 5 percent tariff on Mexican imports beginning on Monday, but stressed that negotiations and deliberations will continue and the paperwork could be withdrawn or shelved.

“I think there is the ability — if negotiations continue to go well — that the president can turn that off at some point over the weekend,” Short told reporters at the White House.

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Short praised Mexican officials for floating new ideas about how to stem the flow of Central Americans traveling to the U.S. over the past two days of negotiations, but said there is still “a long way to go” to satisfy Trump’s demands.

Negotiations are expected to resume on Friday with a Mexican delegation that traveled to Washington earlier this week to stave off the tariffs. Trump has received updates on the talks but has not taken part in them himself, as he has been on a weeklong trip to the United Kingdom, France and Ireland.

“Our position hasn’t changed. Tariffs are going to take effect on Monday,” White House press secretary Sarah Huckabee Sarah Elizabeth SandersSarah Sanders on Trump's reported war dead criticism: 'Those comments didn't happen' Sarah Sanders memoir reportedly says Trump joked she should hook up with Kim Jong Un McEnany stamps her brand on White House press operation MORE Sanders told reporters traveling with the president in Ireland, before noting the talks have been positive.

“They’ve made a lot of progress,” she said. “The meetings have gone well but as of now we’re still on track for tariffs on Monday.”

Trump is planning to declare a new national emergency to impose the tariffs under the 1977 International Emergency Economic Powers Act, according to a draft document obtained by The Hill.

The president announced suddenly last week that he wanted to impose tariffs on Mexico amid mounting frustration over the administration’s inability to curb illegal immigration, one of Trump’s core promises during the 2016 campaign.