CHICAGO (CBS) – Waving purple sheets of paper in the air and chanting “Yes, we can!” about 2,000 union janitors rallied at Teamster City at Ashland Avenue and Jackson Boulevard on Saturday.

The purple sheets of paper signified a yes vote from the members, authorizing their bargaining committee to strike if they can’t come to an agreement with the Building Owners and Managers Association (BOMA).

The janitors’ bargaining committee for SEIU Local 1 is arguing for a better health care plan and better wages. Negotiations have been going on for a month, and their contract expires April 8. They’re scheduled to meet again at the bargaining table this Friday, April 6.

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The contract affects 13,000 janitors in and around Chicago, at commercial office buildings, public schools, malls and city of Chicago facilities.

Some of those offices include Bank of America, JP Morgan Chase, General Electric, CME Group, Boeing, AT&T, Kraft, United and Tishman Speyer.

Local 1 President Tom Balanoff says the economic recovery experienced by bigger businesses in the last few years haven’t come to his members — as the average janitor earns about $31,000 a year. In the suburbs, the average is $24,000. The union cites the Economic Policy Institute’s calculation that the cost of living for a family of four in the Chicago area is $51,319 a year.

The contract covers:

–4,000 janitors in downtown commercial office buildings
–3,000 in suburban commercial office buildings
–2,700 in public schools and City of Chicago facilities
–3,500 in malls, universities and other buildings.