Cross-sector relationship building is an important strategy in corporate social responsibility initiatives, and communicating cross-sector relationships on social media can help raise the visibility of collaborative relationships. A noticeable gap in the literature is how social media enables and constrains the formation patterns of cross-sector connections. To understand how businesses communicate their relationships with government agencies and nonprofits about social issues on social media, we propose a theoretical framework that centers public attention as a critical resource and considers different sectors' (...) interests in the COVID-19 issue. We tested this framework with a nationally representative sample of 1,980 organizations on Twitter. The analysis reveals that the increase in public attention to the COVID-19 issue was accompanied by a greater likelihood of cross-sector ties. Specifically, firms severely affected by COVID-19 were more likely to build ties with government agencies, and the increase in public attention also drove firms to build more ties with nonprofits, especially advocacy nonprofits. Our findings suggest managers of social media communication should observe the volatile public attention and design communicative strategies accordingly. (shrink)