They wrote a letter to the government in which they say: "While many of the arguments for equal marriage are based on rights and equality, there is also an important economic argument."
Companies want their LGBT employees to have the same rights as any other in the UK.
"A diverse, outward-looking and inclusive society is essential to create a vibrant and competitive economy and a prosperous future for Northern Ireland," the letter adds.
These companies come from different backgrounds. There are Coca-Cola Ireland, law firms Baker McKenzie and Pinsent Masons, consultants Deloitte and PwC, Liberty IT, Bank of Ireland and Ulster Bank.
"The business case for marriage equality is compelling, both in terms of retaining and attracting talent, and also to send out a message to international investors that Northern Ireland is a modern, outward-looking economy, with a progressive attitude on personal freedoms and rights," said Andrea McIlroy-Rose of Pinsent Masons.
"We want to do what we can to ensure our customers, colleagues and the LGBTQ+ community in Northern Ireland have the same rights extended to them as the rest of the UK and Ireland," Sandra Wright of Ulster Bank added.
Seven attempts to legalize marriage equality failed. The last one was approved by the assembly and senators but the government vetoed it. Whenever business gets involved in the fight for LGBTQ rights, it helps, so hopefully, their talk will tip the scales.