The U.S. Chamber of Commerce and its union opposition will go head-to-head next week on Capitol Hill, bombarding lawmakers with competing fly-ins as the battle royale over the Employee Free Choice Act continues to intensify.

The latest push will come just days after Vice President Joseph Biden endorsed card check legislation — the union movement’s top priority on the Hill — at an AFL-CIO executive council meeting in Florida.

The legislation, which business groups fervently oppose, would make it easier for workers to unionize by giving them the right to union recognition after a majority of workers have signed pro-union cards.

The Chamber of Commerce is bringing in more than 170 people from state and local chambers in Louisiana, Nebraska, Pennsylvania and Virginia.

The lobbying effort is part of its kick-off of a new grass-roots advocacy initiative that will include several “Workforce Freedom Airlifts,— what the Chamber is calling its fly-ins, according to Chief Financial Officer Steven Law.

The Chamber is also doing print and television ad buys in each the four states and inside the Beltway.

“The momentum clearly seemed to have moved in our favor at the beginning of this year,— Law said. “[But] there is no question that organized labor is gearing up their efforts as well. Our view is that we need to be every bit as present and active as they are in this next phase,— he added.

While the Chamber is holding meetings with state and local representatives on Monday, the unions are kicking off their own legislative action.

More than 300 union workers from across the country are expected to attend a rally across the street from the Chamber’s headquarters in Lafayette Park.

As part of SEIU’s Change That Work’s Campaign, union members are planning on meeting with their state Congressional delegations on Tuesday.

The fly-in is also being used to train workers for a mass mobilization in more than 50 cities planned for March 19, said SEIU spokesman Mark McCullough.

“We’re definitely going to make sure that lawmakers continue to hear from the voters in their District,— McCullough said.