The group, which has been marching along roadsides and railways in the southern Mexican state of Oaxaca, is being organised by US-based Pueblo Sin Fronteras (People Without Borders).
USA presidents have ordered National Guard forces to the border in the past.
He's been complaining that USA borders are too porous and its immigration laws are too weak.
President Trump reiterated his Easter Sunday warning about "caravans" of immigrants traveling through Mexico to the United States border in a Twitter thread Monday and called on Congress to pass legislation to "stop the massive inflow of Drugs and People".
These "Stations of the Cross" migrant caravans have been held in southern Mexico for at least the last five years.
And while Office of Government Ethics guidelines prohibit donations from lobbyists or others with governmental interests, the Patriot fund says donations for legal expenses would be banned only if the donor "indicates in writing that the contribution is being given because of an eligible recipient's position or performance of duties".
In a post on Twitter, he had said the caravan "heading to our "Weak Laws" Border, had better be stopped before it gets there". The $1.3 trillion spending package recently passed by lawmakers only includes $1.6 billion for border wall funding, and the bulk of that money must be used to fix existing parts of the wall, not for new construction. "It's like we have no border". Trump claimed the potential militarization of the border was necessary due to the lack of his proposed border wall or proper security. The segment was a follow-up to a report by Buzzfeed News on hundreds of Central Americans making their way through Mexico in hopes that American authorities will grant them asylum or be absent when they attempt to cross the border. The caravans typically don't proceed much farther north than the Gulf coast state of Veracruz.
By calling for Republicans to use the "Nuclear Option" to pass tough new immigration measures, Trump seemed to urge a parliamentary procedure by which Senate Republicans could pass legislation with a simple majority of 51 votes as opposed to the 60-vote majority required to end debate and bring a vote to the floor.
Constructing a "big, handsome wall" along the Mexican border was a signature campaign promise for Mr Trump, but so far the plan to erect a new physical barrier has been thwarted by lawmakers and appears to have stalled. Most of it can only be used to fix stretches of the border where there already is a wall, not to build new segments. Under current law, unaccompanied children from countries that don't border the USA are turned over to the Department of Health and Human Services and undergo often lengthy deportation proceedings before an immigration judge instead of being immediately deported. Congress also put restrictions on the types of barriers that can be built. Officials complain that many children never show up at their hearings. But Senate Majority Leader Mitch McConnell has dismissed that option in the past, saying Republicans will welcome the filibuster when they return to being the Senate minority.
The proposals appear the same as those included on an immigration wish list the White House released in October but failed to gain traction during negotiations over the border wall. But Trump appears intent on ensuring the issues remain at the forefront of public conversation, even though the omnibus was widely seen as the last major legislation likely passed this year. "They must stop them at their Northern Border, which they can do because their border laws work, not allow them to pass through into our country, which has no effective border laws", he wrote.