The United States and Mexico have been engaged in detailed negotiations throughout the week, as the Trump administration seeks a new agreement on trade in addition to cooperation from the Mexican government to block illegal immigrants from crossing the U.S.-Mexico border.

Just as President Trump is set to impose a new 5 percent tariff on all Mexican imports on Monday, should Mexico fail to take adequate measures to stop migrants from Central America crossing into the United States, he announced today through Twitter that Mexico may have another option to avert the tariffs—by purchasing more U.S. agricultural products.

While returning from Europe aboard Air Force One, Trump tweeted, “If we are able to make at the deal with Mexico, & there is a good chance that we will, they will begin purchasing Farm & Agricultural products at very high levels, starting immediately. If we are unable to make the deal, Mexico will begin paying Tariffs at the 5% level on Monday!”

It would appear that the president aims to complete a comprehensive agreement between the United States and Mexico that combines both an agreement on trade and measures to counteract illegal immigration. Negotiations between the two countries are expected to continue through the weekend, right up until Monday’s deadline before tariffs are to be implemented.

If this is the case, Trump’s announcement would also indicate a shift in the administration’s strategy in U.S.-Mexico negotiations since just yesterday, when negotiations centered around illegal immigration exclusively and White House press secretary Sarah Huckabee Sanders told reporters, “Our position hasn’t changed. The meetings have gone well, but as of now we’re still on track for tariffs on Monday.”

If it turns out that the Trump administration is indeed pivoting in its negotiations with Mexico, Trump may doing so, in part, due to political pressure from within both parties not to declare a national emergency at the U.S.-Mexico border, something that would be required to invoke executive powers under the International Emergency Economic Powers Act. Some senior legislators have expressed concern that the president would be exceeding his executive authority if he were to declare a state of emergency with the aim of imposing economic sanctions on Mexico.

Just last week, when Trump announced his intention to impose tariffs on Mexican imports, Sen. Chuck Grassley (R-Iowa), chairman of the Senate Committee on Finance, objected, stating, “This is a misuse of presidential tariff authority and counter to congressional intent. I support nearly every one of the President Trump’s immigration policies, but this is not one of them.”

In particular, Sen. Grassley felt that Trump’s new tariffs on Mexican imports could “seriously jeopardize” the administration’s hard-fought NAFTA agreements with both Canada and Mexico forged during the past year.