Any person, organization, or PAC that is making contributions directly to federal candidates must comply with the applicable federal contribution limits, outlined below:
Individuals can contribute up to $2,900 per candidate per election.
Political Action Committees (PACs) can contribute up to $2,900 per candidate per election, but that limit increases to $5,000 for PACs that achieve Multi-Candidate status.
Corporations, including many 501(c)(4)s, are prohibited from making direct contributions to candidates, which includes monetary and in-kind contributions as well as coordinated expenditures. Corporations have the option to form a Separate Segregated Fund (SSF), a special type of PAC account that is connected to the corporation but is also able to make contributions to candidates, including coordinated expenditures. For more info on SSFs, check out this FEC webpage.
For the purposes of calculating federal contribution limits, each primary or general election is considered a separate election.
For more detailed info on federal contribution limits, check out this FEC webpage.