The current method for workers to form a union in a particular workplace in the United States is a sign-up then an election process. In that, a petition or an authorization card with the signatures of at least 30% of the employees requesting a union is submitted to the National Labor Relations Board (NLRB), who then verifies and orders a secret ballot election. Two exceptions exist. If over 50% of the employees sign an authorization card requesting a union, the employer can voluntarily choose to waive the secret ballot election process and just recognize the union. The other exception is a last resort, which allows the NLRB to order an employer to recognize a union if over 50% have signed cards if the employer has engaged in unfair labor practices that make a fair election unlikely.

Under the proposed Employee Free Choice Act (EFCA), if the NLRB verifies that over 50% of the employees signed authorization cards, the secret ballot election is bypassed and a union is automatically formed. Introduced in the U.S. Congress in 2005 and reintroduced in 2007 and 2009, the EFCA provides that the NLRB would recognize the union's role as the official bargaining representative if a majority of employees have authorized that representation via majority sign-up (card check), without requiring a secret ballot election. Under The EFCA, if over 30% and fewer than 50% of employees sign a petition or authorization cards, the NLRB would still order a secret ballot election for union representation.

Card check is not new. Since the National Labor Relations Act was passed, it has been legal for workers to form a union when a majority of employees in a bargaining unit sign cards indicating their intent to bargain collectively with the employer. According to a recent law review article, the National Labor Relations Board in its early days "certified on the record when there had been an agreement with the employer for card-check." It adds that "in the final year before the Taft-Hartley Act was passed [in 1947], 646 representation petitions were informally resolved through the card-check procedure."

In 1969, Chief Justice Earl Warren delivered the majority opinion for the U.S. Supreme Court that upheld the use of majority sign-up (card check). Warren stated, "Almost from the inception of the Act, then, it was recognized that a union did not have to be certified as the winner of a Board election to invoke a bargaining obligation; it could establish majority status by other means... by showing convincing support, for instance, by a union-called strike or strike vote, or, as here, by possession of cards signed by a majority of the employees authorizing the union to represent them for collective bargaining purposes." NLRB v. Gissel Packing Co., (1969). The Supreme Court has consistently ruled in favor of majority sign-up (card check), and Warren cited prior affirmations in NLRB v. Bradford Dyeing Assn., (1940); Franks Bros. Co. v. NLRB, (1944); United Mine Workers v. Arkansas Flooring Co., (1956).

Supporters of card check argue that it makes it easier for workers to join unions. For example, in his remarks accompanying the introduction of the Employee Free Choice Act, Rep. George Miller (D-Calif.), chairman of the U.S. House Committee on Education and Labor, described the limitations of the system of NLRB elections:

Even when employers don't break the law, the process itself stacks the deck against union supporters. The employer has all the power; they control the information workers can receive, can force workers to attend anti-union meetings during work hours, can require workers to meet with supervisors who deliver anti-union messages, and can even imply that the business will close if the union wins. Union supporters' access to employees, on the other hand, is heavily restricted.

The Employee Free Choice Act [with its provisions for majority sign-up] would add some fairness to the system…

Barack Obama supports the bill. An original co-sponsor of the Employee Free Choice Act, then-Sen. Obama urged his colleagues to pass the bill during a 2007 motion to proceed:

The AFL-CIO states the following in arguing that the company-controlled secret ballots actually make the process less democratic:

Those who oppose card check argue it strips workers of their right to a secret ballot. They also argue that even though gathering a majority of card signers might imply that a secret ballot would be unnecessary, signers could be coerced to sign through intimidation and pressure, making it an inaccurate mechanism for determining employee support for unionization. Many business organizations, including The U.S. Chamber of Commerce, oppose the implementation of card check. From its website: