While trade-related bills may originate in either the Senate or the House of Representatives, Article I, Section 7 of the Constitution provides that all bills for raising revenue (e.g., legislation that affects tariff rates or other import charges) must originate in the House. Bills may be introduced by any member of the House or Senate. Once a bill is introduced, it is referred to the committee or committees that hold jurisdiction over the matter addressed by the legislation. Trade-related bills are almost invariably referred to the Committee on Ways and Means on the House side and the Committee on Finance on the Senate side. Other committees that may consider trade-related bills include, but are not limited to, the House Committees on Homeland Security, Energy and Commerce, and International Relations, and the Senate Committees on Commerce, Science and Transportation, Foreign Relations, and Homeland Security and Governmental Affairs.

Bills need to be approved by both the House and Senate and signed by the president to become law. The House and Senate have similar mechanisms for considering legislation although several significant procedural differences exist. In each case, after a bill is introduced and referred to the relevant committee, it can be referred to a subcommittee for consideration. The committee chairman has significant leeway over the committee schedule and, as such, holds considerable power over the bills that are considered by the committee during the legislative year. One of the first actions taken by a committee is to seek the input of the relevant departments and agencies about a bill. Frequently, the bill is also submitted to the Government Accountability Office with a request for an official report on the necessity or desirability of enacting the bill into law. In necessary, the committee or subcommittee may also hold public hearings on the legislation.

After hearings are completed, the subcommittee will usually consider the bill in a so-called "mark up" session. The subcommittee may decide to report the bill favourably to the full committee (with or without amendment), unfavourably, or without recommendation. The subcommittee may also suggest that the committee "table" the bill or postpone action indefinitely. The same process is repeated at the full committee level. It should be noted that the House and Senate both have the ability to discharge a bill from committee without a vote, although this authority is not frequently used.

Bills reported from committee are placed on one of four action calendars in the House and one of two action calendars in the Senate. The speaker of the House sets the legislative schedule in conjunction with the majority party leadership and selected representatives and, as such, holds considerable power over the legislation that is considered. The majority leader has the authority to raise legislative measures in the Senate, although this is usually done in broad consultation with minority party leaders and interested senators.

While substantial differences exist in how the full House and Senate consider and approve legislation, in essence each chamber will debate a bill scheduled for consideration and then hold a vote. The legislation may be approved with or without amendments. In the case of bills approved by the House, the bill in question is engrossed (i.e., a final draft is printed) and forwarded to the Senate. In the case of bills approved by the Senate, the bill is forwarded to the House unless it is held by unanimous consent to become a vehicle for a similar House bill if and when passed by the House. Bills approved by the House are referred to the relevant committee in the Senate, and vice versa, and the legislation is considered in accordance with the rules of that chamber. If a bill approved by one chamber is approved by the other chamber without any amendments, it can be enrolled and forwarded to the president for signature. However, if a bill approved by one chamber is approved by the other chamber with amendments, it is returned to the originating chamber for further consideration. The originating chamber may agree to the amendments or request a conference to resolve any disagreements. Once a consensus is achieved in conference, the bill is enrolled and forwarded to the president.

Bills approved by Congress are presented to the president for signing. The president may, within 10 days and at his sole discretion, sign the legislation into law or veto it. If the legislation is vetoed, a two-thirds majority vote in both the House and Senate is needed to override the veto. In cases where Congress has adjourned for the legislative session prior to the expiration of the 10-day period required for presidential action and the president does not wish to sign the bill, he may take no action and the bill will be considered vetoed without possibility of override and without the president having to list his objections. This is known as a pocket veto.

Another important role of Congress is its consideration of international agreements negotiated by the Administration that require changes to US trade laws. While Congress has the constitutional prerogative to amend any such agreements as it sees fit, it temporarily gave up this authority in 2002 with the passage of trade promotion authority (TPA). TPA thus allows the Administration the freedom and flexibility to negotiate trade agreements without having to worry about congressional amendments that could ultimately prove unacceptable to US negotiating partners. In return for this freedom of action, the Administration is required to, among other things, pursue certain negotiating objectives, meet certain notification requirements, and hold consultations with Congress regarding (i) the nature of the agreement; (ii) how and to what extent the agreement will achieve the applicable purposes, policies, priorities and objectives; and (iii) the implementation of the agreement, including its general effect on existing laws.

TPA is scheduled to expire on 1 June 2007.