I see two ways of interpreting the situation of non-tenure-track faculty, drawing from Marx in Capital. If we think of higher education as an industry, and a university as a capitalist enterprise on the factory model (obviously, omitting layers of exchange between the “non-profit” sector of higher ed and overall social capital and accumulation), then tenure-track faculty are regular faculty workers and non-tenure-track faculty can be understood either as cottage industry “piece work” laborers, or as an industrial reserve army. These are not mutually exclusive, I believe.
Cottage industry, as Marx used the term, refers to production taking place outside of the factory. Marx distinguished ordinary cottage industry in which the commodity products of factories are transformed into more finished commodities by individuals with specialized abilities or at the convenience of the industrial capitalist, from cottage industry taking place as after-hours piecework by ordinary wage-laborers. Either form of cottage industry applies to non-tenure-track labor.
As routine, non-tenure-track faculty are often relied upon as labor for specific functions outside normal production of the university. At Cow State Santa Claus, many work as “special consultants” on special projects, to score qualification exams of various kinds, etc. Tenure-track faculty also avail themselves of these “opportunities,” including working in summer sessions through the for-profit extended education unit. Because faculty wages are held below what affords many faculty a reasonable income for their various debts, the university creates the need for additional wages for subsistence. This is similar to mandatory overtime, or extension of work-time.
But many non-tenure-track faculty do cottage labor of a different sort, producing themselves as means of production, by preparing courses that they may or may not teach, doing research and other work without compensation or paid expenses to maintain field currency, contributing to their field’s base of knowledge, etc. Unlike tenure-track faculty who are at least nominally paid for this work, and who can typically predict what classes they need to prepare to teach and thus what areas they need to be current in, non-tenure-track faculty simply have to be ready, or else their labor will lose its saleable value. This is specialized work performed entirely outside the factory setting, and only paid on the basis of its sale as ready labor-power.
That is also the condition of the industrial reserve army. To maintain low wages, it is necessary that there always be a large stock of ready labor-power that is unemployed or underemployed. The value of labor as a commodity is lowered by this reserve stock. The costs for developing and maintaining that labor-power are unpaid, or paid via charity or social welfare systems. Capitalists call upon this reserve at the moment it is needed, and dispose of it as soon as possible. As a reserve, workers in this class are themselves immobile, but to the capitalist, transferrable and exchangeable at whatever distance and to whatever locale. The workers experience their relation to the means of production as interrupted and fleeting; for the capitalist, this labor-power is always available.